One glaring omission in US Gamer's story last August on PC games playable on low-spec systems was the enormous selection classic PC games available digitally these days. That selection is far too vast for just one article to pick out the best ones. One interesting category to observe however is the classics that had the most influence on the popular games of today.
Many of today's most successful PC and console games like BioShock, Elder Scrolls, or Fallout are actually sequels, spiritual successors, or were at least heavily inspired by PC games made throughout the 90's and early 2000's. Most of them were made by some of the same staff, who didn't start making games on consoles until the Xbox came around. Almost all of those older games are available to buy and download at places like Steam, GoodOldGames, or Amazon for low prices, especially during holiday sales. Although their graphics are obviously dated, their gameplay systems tend to hold up very well to modern scrutiny, often proving to be more complex and more open-ended than their modern successors, though they may take slightly more time to learn. If you're looking for quick access to more games like some of your favorites from today, looking up their predecessors might be a good idea.
No computer built within the last five years, if not the last decade, lacks the horsepower to run these games, though some may require mods to avoid errors on modern systems (which will be described below).
Ultima Underworld (1992) and Ultima Underworld II (1993)
Play if you like: BioShock, Fallout, Dishonored, Deus Ex Human Revolution, Elder Scrolls, Dark Souls
Ultima Underworld is the reason games like Elder Scrolls, Fallout 3, Deus Ex, and BioShock exist. It was one of the first games to blur the line between first person action and role-playing. Even From Software's dark fantasy RPGs, from King's Field to Dark Souls, are direct descendants of this game.
Released about a year before DOOM, Ultima Underworld: the Stygian Abyss is credited with pioneering the mechanics that attempt to simulate realistic, dynamic 3D worlds. Similar to Bethesda's games like Fallout 3 and Skyrim today, Underworld let's players generally interact with the world as they please, including most objects, non-player characters, and the general progression of the story itself. The conversation system in particular is unmatched by even most of today's games.
Underworld however doesn't take place in a completely open world, but rather a labyrinthine series of eight levels that make up the underground ruins of a failed utopia -- essentially BioShock 15 years before BioShock. Each level of the Stygian Abyss is occupied by different quarreling factions players have to barter with while exploring, and exploration here is quite nonlinear.
Ultima Underworld II: Labyrinth of Worlds tightens up the first game's interface and art direction, but more importantly increases the variety of places to visit. Instead of one world split into levels, Underworld II takes players through smaller pieces of several worlds, each with its own quests, characters, and factions to navigate, though it is a slightly more linear game.
This article might be about retro games, but Underworld and its sequel are by far the oldest games mentioned here and thus are the least accessible. Their gameplay mechanics are similar to many of today's RPGs, but the controls take getting used to and the graphics look like DOOM. These two games are also the only ones in this article that don't have in-game tutorials. They're from the days when games expected you to read manuals (which come included on GOG). Another warning is that both games, in their nonlinear and dynamic nature, don't care too much about players getting permanently stuck, so multiple save files are almost a must.
On GOG the games come with a DOS emulator and require nothing else to get running. There is a PS1 version of the first game but it's Japan-only.
Arx Fatalis (2002)
Play if you like: BioShock, Dishonored
If the Underworld games' graphics and interface prove a little too old-school but their core mechanics still seem interesting, Arx Fatalis might be a better choice. It's essentially the unofficial sequel to those games but was made a lot closer to modern times. The Elder Scrolls III: Morrowind simply overshadowed Arx when it came out.
The first game from Arkane Studios (Dishonored), Arx is also set in a massive subterranean community split into levels which players can explore with a lot of freedom very early on. It has its own web of races and tribes players have to investigate, negotiate with, and steal from. From a console gamer's perspective, exploring Arx kind of feels like a 3D Metroidvania despite it probably having no deliberate connections to that style of game design.
Unlike Underworld though, Arx features your standard first person WASD controls and a more straightforward inventory system. The magic-casting system is similar to Underworld's runes that work together in a complex system players have to learn, but requires they draw them on the screen dynamically. Stealth is also much more robust in Arx.
Running Arx on modern computers however does pretty much require a source port called "Arx Liberalis," otherwise the game runs too quickly on today's processors. Installing it just requires activating an exe file after installing the base game. There's a version for the original Xbox but it's not 360 compatible.
Thief (1998) and Thief II (2000)
Play if you Like: Dishonored, Splinter Cell, Thief (2014)
Anyone who's been playing Dishonored or the new Thief should at least investigate the first two games. Considered two of the best stealth games ever, Thief: The Dark Project (and its expanded version Thief Gold) and Thief II: The Metal Age have mechanics that still stand out compared to the rest of the genre and level design that often surpasses most modern stealth games in size and depth.
Instead of taking you from waypoint to waypoint, classic Thief simply throws players into its levels with multiple simultaneous objectives and leaves them to make their own plans for completing them. Some might find structural similarities between classic Thief and GoldenEye or the original Perfect Dark, which were big influences.
The first game has quite a bit of variety in terms of where players go and what they do. They might start out stealing valuables in mansions, but pretty soon they end up dodging zombies and evil spirits in ancient ruins and haunted cities Indiana Jones style.
Both games use light and sound as a central element. Different movement speeds and the properties of various surfaces affect how much sound you make to attract guards, and staying in the dark is imperative. The tools players get are usually geared towards that end.
Thief II: The Metal Age (2000) stays true to the first game but ramps things up with new tools and even more daunting level design. With barely a tutorial to warm you back up from the first game, Thief II almost immediately has you sneaking through what are still some of the biggest levels in stealth games.
The old Thief games do require fan-made mods to properly run on modern Windows but they're not too obtuse, and are included on GOG. A benefit of this is that there are optional mods that let you install better looking textures and even fan-made missions. In terms of controls, Thief Gold's default control scheme is slightly unusual but can be remapped. Both games actually can recognize an Xbox 360 controller if the "joystick" option is turned on in the options menu, but the buttons have to be mapped manually.
The Dark Mod (2009)
The Dark Mod is a fan-made attempt to bring Thief's mechanics and spirit into a more modern game engine. Until recently it required a copy DOOM 3 to run, but is now available on its own for free.
Mechanically, it pretty much is Thief II running on the DOOM 3 engine. That engine however brings things like dynamic lighting and a physics engine to the game, which the designers ensured players could use to more freely manipulate light and objects. The enemy AI also got a bit of a boost in Dark Mod compared to Thief II.
The initial Dark Mod download only comes with a training mission and a single fan mission, but more can be downloaded from within the game, all free. As of this writing, more than 50 fan missions and even some fan campaigns have become available.
Deus Ex (2000)
Play if you like: Deus Ex Human Revolution, Fallout, Dishonored
Of all the games on this list it probably makes the most sense for fans of Deus Ex's modern successor to go back and try the original. The obvious reason is Human Revolution is a prequel to the first game. The original however also has a somewhat deeper, more RPG-like feel to its gameplay.
Deus Ex combines the simulated worlds of other RPGs with the stealth/FPS balance (one of the Dishonored level designers worked on Deus Ex) and cyberpunk suspense storyline seen in Human Revolution. The combat and other elements however are much more balanced towards the RPG end of the scale.
Not only do players buy and upgrade cybernetic augmentations like in Human Revolution, but they also spend skill points on stats like medical, computers, lock picking, and five areas of weaponry (tip: don't invest in swimming). Players also have individual health bars for each part of the main character's body. On the surface it actually looks like the same system seen in Fallout 3 and New Vegas.
One thing clearly better in the original than Human Revolution is boss fights. In the original, the bosses got a lot more character development throughout the game, and throughout the story players have multiple chances to fight them or avoid them altogether.
Running Deus Ex on modern Windows does require a fan-modified renderer, otherwise it runs at an unnatural speed on multi-core processors. Installing it is as simple as dropping some files into the main game folder in Windows Explorer. There are also mods to improve the textures. Earlier this year someone actually released an entire fan-made campaign with original music, voice acting, and even new weapons along with several hours of new gameplay. Even the developers of Human Revolution acknowledged it. Deus Ex also has a PS2 version that's available on PlayStation Network for the PS3.
System Shock 2 (1999)
Play if you like: BioShock, Dead Space
System Shock 2 (1999) is probably the most critically-acclaimed game on this list, and that's saying something. The direct spiritual predecessor to BioShock, SS2 features the same basic mechanics and storytelling style but with a sci-fi theme and gameplay more focused on role-playing and survival horror than shooting.
Instead of an underwater city, SS2 takes players through the various decks of a space ship where they fight zombies, cyborgs, and other monsters while piecing together the storyline from audio logs and environmental cues. If that sounds kind of like the first Dead Space, there are actually a lot of curious similarities between the two games, and Dead Space is rumored to have begun development as System Shock 3.
Taking place in yet another simulated RPG world, SS2 feels somewhat similar to the early Resident Evil games, just in first person. It has players deal with a limited inventory as opposed to BioShock's automatic item consumption and limited resources. On default settings, weapons even break down and have to be repaired or replaced.
SS2 has pretty deep character-building elements too. The game's somewhat tedious tutorial segment lets players choose from one of three character classes. Throughout the game players have to spend experience points (which are limited) on stats like strength, endurance, or agility. They also have to upgrade skills like hacking or item research.
SS2 has an online co-op mode as well
Running SS2 on today's computers used to require a cocktail of mods, but the recent Steam and GOG releases automatically install everything necessary, so it's just plug n' play. However, there are still optional graphics mods. The game is also available on Mac.
Of course the subject of retro PC games encompasses around three decades of games, of which the aforementioned are a tiny portion. These games however, are some of the most pertinent and relevant to gamers who've been playing some of today's first person shooters and RPGs. Even beyond the interest in seeing the history of the games, these classic works still offer a lot of critically acclaimed gameplay that you won't see in modern games.