VVVVVV
Platform: PC, Mac, Linux, Nintendo 3DS
Release date: 2010
This is such an awesome game. VVVVVV is a hardcore platformer with a really strange title (I'm not even sure how to say it!). This game features simple, 8-bit style graphics, an innovative reverse-gravity gameplay mechanic, a cute storyline, and an awesome chiptune soundtrack.
I picked this game up as part of the third Humble Indie Bundle a number of months ago, but the game was actually released in 2010. It's taken me a while to clear up some of my gaming backlog to get to this game, but it's popularity and great reviews are well deserved.

It is very hard, though. Keyboard-smashing, dog-kicking, teeth-gridingly hard. But, like most old-school platformers, it just makes successful platform jumps that much more sweet and rewarding.
VVVVVV is a Flash game that's been backported to C++, but you'd never know it. What's more: people on all computer platforms are able to play this game: PC, Mac, and Linux support comes out of the box. The game was also released on the Nintendo 3DS, but I haven't had a chance to try that version out.
If you like platformers the way they used to be, you can't do much better than VVVVVV.
Play the demo | Get the game ($5!) | Listen to the soundtrack