I've found that I like platformers with very hard but short levels (so you don't lose a ton of progress when you die, and can thus die hundreds of times trying to beat a single level without getting too frustrated). Recently: League of Evil (the sequel isn't as good, unfortunately) and Super Meat Boy.
Super Hexagon warps my perspective, though it's not a traditional platformer. In my first 30 minutes of playing, I managed 26 seconds.
This is the monthly thread for posting media of various types that you've found that you enjoy. I find that exposure to LW ideas makes me less likely to enjoy some entertainment media that is otherwise quite popular, and finding media recommended by LWers is a good way to mitigate this. Post what you're reading, listening to, watching, and your opinion of it. Post recommendations to blogs. Post whatever media you feel like discussing! To see previous recommendations, check out the older threads.
Rules: