The original Half-Life has a bad ending. I'm not referring to the alternate ending, where the enigmatic G-Man tosses the player into a room full of enemies as a "screw you" for not taking his "job offer." I mean the way Half-Life brings its story to a close, period. I don't hate all of the Xen levels, nor do I dislike the move of introducing the G-Man at the last minute—what I really dislike is just how abrupt and open ended it is. You travel to another dimension, kill a giant alien mandrake, and then you're just dumped into stasis. What, exactly, was it all for?
Half-Life 2, which is celebrating its 15th anniversary, improved upon the original by delivering a slightly better cliffhanger. Within the first few minutes of Half-Life 2, you're introduced to the cruel regime of the Combine. At the game's end, Gordon Freeman and Alyx Vance strike a critical blow against the oppressors after igniting the first significant rebellion in years. Then, and only then, does the G-Man pop in to put the player away again. Still frustrating, but at least you know you accomplished something.
Then, of course, the Half-Life 2 Episodes came along and messed things up.
"The decision to break into episodes wasn't really driven by story requirements," said Valve co-founder Gabe Newell in an interview with IGN around the time of Episode One's release. "The story sort of ended up being fit into three buckets. Typically, in any of these larger arcs, it's not too surprising you can think of them as three acts."
Three acts that, as you're surely aware, have never been completed. With neither a Half-Life 2: Episode Three or a proper Half-Life 3 to ever bring a close to the story of Gordon Freeman, Alyx Vance, and the human resistance's struggle against the Combine, the series is left hanging on an incredibly unsatisfying note (notwithstanding series writer Mark Laidlaw's coda).
You could fill volumes with what's been written about the void left after the end of Half-Life 2: Episode Two, but hey: today isn't its anniversary. When I consider the ending of Half-Life 2 now, in a vacuum sans Episodes, I like it a whole lot more than I used to.
It's still far from perfect. The fates of Alyx, her father Eli, and Dr. Judith Mossman are left unclear. It sure seems like Dr. Breen is dead, but you're not quite sure about that either. Is blowing up one Combine reactor in City 17 really all that much of a victory? How many other cities are there, and how outgunned are the freedom fighters who've just lost their Crowbar-swinging hero? Questions, questions, questions.
All the same, Half-Life 2's ending is still far less open-ended than the ways the original Half-Life and Episode Two wrap up. Half-Life leaves you with the haziest sense of what you've accomplished—you never learn how far the alien invasion has spread beyond the walls of Black Mesa. Episode Two tells you where you're going, shows you what you're about to do, and then rips away a beloved character in a scene I still find hard to watch. One tells you too little, the other tells you too much about what's to come.
At some level, Valve was wary of getting people's hopes up for a third act. In 2007, Episode Two's project lead David Spreyer told Rock Paper Shotgun why Valve didn't make a teaser trailer for Episode Three:
If you look at the Episode Two trailer that we shipped with Episode One there's some pretty radical difference between what you see there and see in finished game. That's really an artefact of making a trailer for a product that's still in heavy production. You just don't know where you're going to end up.
The ending of Half-Life 2 is a result of Valve not knowing where it would end up. Not planning on making Episode One, which picks up right where Half-Life 2 ends, Valve just took a note from the original Half-Life and wrapped things up abruptly. Having the ending serve as a callback to the original game, and as a bookend to Half-Life 2's opening, is just barely enough that it feels like a proper conclusion to your journey. The last thing you see is a door closing—the game's way of saying "we're done here, goodbye." With nothing to guarantee, Half-Life 2's ending guarantees nothing.
I'm reminded of a line from another 2004 game that wrapped up it's story quite suddenly: "Don't make a girl a promise if you know you can't keep it." Half-Life 2's ending promises you nothing, and it's the best in the series for it.