One of the nicest things about the Nintendo 3DS is that you don't have to spend a lot of money to get quality games. The Nintendo 3DS eShop has a host of sweet titles that are under ten bucks. Here are some examples, and keep in mind these are base prices; you can find them even cheaper during a sale.
When Nintendo first entered the prickly territory of free-to-play games, the company stressed its offerings weren't going to be "free-to-play" so much as "free-to-start." That describes Stretchmo perfectly, as you get its opening tutorial levels for zero dollars and then decide if you want to pay up for more.
If you're already a fan of this excellent block-based puzzle series, then you're definitely going to want to pony up for more good times with Mallo. The same push-and-pull mechanics that define Pushmo and Crashmo are present, but now there's a little horizontal stretching action as well. Give it your best squishy-sumo try.
BOXBOY! ($4.99 USD)
Part of being a hero is finding ways to surmount your problems in spite of your own limitations. That's the premise driving BOXBOY!, a clever puzzle / platforming game from HAL Labs.
Boxy little Qbby isn't very good at running or jumping, but he's a champ at spawning boxes from his own body (let's not think too hard about the biology behind this act). It's that box-spawning ability that lets him vault over high walls, move across spiked pits, trigger traps, and defend against hazards. BOXBOY! is quite different and very charming, more or less what you'd expect from HAL.
3D Out Run ($5.99 USD)
As you may well already know, Sega's Out Run isn't a racing game; it's a driving game. Yu Suzuki's arcade classic from 1986 is still celebrated for simultaneously offering an intense challenge while letting players soak in the game's speed, soundtrack, bright visuals, and iconic characters.
M2's excellent port of Out Run makes full use of the Nintendo 3DS's 3D functionality. It also runs at twice the original game's speed (60 FPS versus 30 FPS) and has a host of additional features like difficulty settings and car customization options.
3D Sonic the Hedgehog ($5.99 USD)
Sega's blue rodent hardly needs an introduction, and neither does his very first game. It was worth playing on the Sega Genesis in 1991, and it's still worth playing on the Nintendo 3DS now.
Of course, M2 deserves a shout-out for the loving care it put into Sonic's 3DS port. Sonic now has access to the Spin Dash -- a spin-out move that wasn't part of Sonic's repertoire until Sonic the Hedgehog 2 -- and there's a stage select option that lets you leap past your most hated levels. Take a hike, Labyrinth Zone. Nobody likes you.
Steamworld Dig ($8.99 USD)
There's something cathartic about digging a hole, and oh boy, does Steamworld Dig ever give you a hole to pick your way through. This unforgettable action / adventure game puts you in the brass boots of Rusty, a steam-powered robot who digs, digs, and digs some more while he unravels some unsettling secrets his late uncle left behind.
All that digging means you uproot tons of precious stones and gems, which can go back into upgrading Rusty. Steamworld Dig is definitely a must-play, as slamming a pick into the hard ground -- and into enemies -- is indescribably satisfying.
Crimson Shroud ($7.99 USD)
Level-5's Crimson Shroud doesn't get the attention it deserves. This unique hybrid blends gamebook-style storytelling, table-top RPG mechanics, and dice-rolling with more conventional digital JRPG gameplay; a pretty brave mix. Though a bit on the short side, it offers an experience that's quite unlike anything available on the eShop.
It's also the handiwork of talented developer Yasumi Matsuno, whose previous games include Final Fantasy XII and another under-appreciated RPG, Vagrant Story.
VVVVVV ($7.99 USD)
VVVVVV stars the strapping young Captain Viridian, who's on a quest to find the members of his space ship crew after they're scattered by an accident. Modelled heavily on Commodore 64 games of old, VVVVVV's platforming quickens the heart, to say the least. Thankfully, frequent checkpoints, a clever sense of humor, and an amazing chiptune soundtrack keep the action super-fun until the very last rescue.
Cave Story ($7.99 USD)
Cave Story by Daisuke "Pixel" Amaya was the go-to example of an indie game before the term "indie game" was widespread. Though initially published over a decade ago, this 2D mechanical blend of Metroid, Mega Man, and Castlevania deserves every word of reverence it continues to garner. It even has a story about killer rabbits that it plays totally straight -- and with great success.
Retro City Rampage: DX ($9.99 USD)
"What if Grand Theft Auto was 8-bit?" is a question that's been asked in many fan videos across the years, but Retro City Rampage: DX makes the question a chunky, pixel-based reality. This open-world adventure game is stuffed with tons of stuff to break, bash, and beat up, and it's all jammed amongst some pretty hilarious references to '80s and '90s pop culture.
Gunman Clive / Gunman Clive 2 ($1.99 USD / $2.99 USD)
Gunman Clive and Gunman Clive 2 are two bullets in the same chamber, so they're worth mentioning in one breath. Both games from Hörberg Productions are budget-priced platformers inspired by the likes of Mega Man and Bionic Commando, though its sketch-style graphics are quite unlike anything else out there (aside from a certain music video by a-Ha). Gunman Clive is a great warm-up for Gunman Clive 2, which features bigger, badder bosses and a fat panda mount.