So I've been playing a lot of Spelunky lately.

It's a procedurally generated, two-dimensional, side-scrolling platformer.  Except it's also a roguelike, as there are no saves, and dying deposits you right back at the start of the game. Except it doesn't, really, as the procedural generation means you're essentially at the start of a new game...

It's free, and it's just seen its final release.  Honestly?  On the indie games landscape, I'd say it's pretty much at the top.  Braid?  Too obtuse at times, despite being brilliant.  World of Goo?  Stunning, evolutionary and pretty much perfected, but honestly? I got bored after a bit.  I've been playing Spelunky right through its open beta all year.  I'm sure I've put more hours into it than anything else this year, and I'm still hooked.

For goodness' sake, try it out.  www.spelunkyworld.com.  Delightfully, it's getting an XBLA release next year, where I'm sure it will flourish.