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Tiny Skater HD is a great platforming game with retro graphics as well as classic retro difficulty. It's great to look at, and feels very old school, but it's a punishing game that requires perfection born through trial and error.
There's no story of any kind, but it's a great arcade-style game that focuses on challenging levels and completion time. It's hard to get used to, but once you do, and once you figure out the perfect way to roll through a level, it quickly becomes addicting.
In the game, you're constantly moving, and there's no way to stop. You can, however, bump into walls or keep turning around like a dog chasing its tail to build up speed, which is actually necessary to play several levels. There are rails to grind in, which don't switch directions; grass that slows you down; and puddles of water to fall into. Apparently, you're made of salt, as water dissolves you and sends you back to the start of a level. The only way to finish a level is to collect every coin-thingy, so don't skip any.
This game is just punishingly difficult. The timing for jumps has to be perfect in the later levels. There's one level in particular that is infuriating gamers everywhere, and that is level 25. It features half a dozen extremely difficult jumps, all in very near succession, and it's painful. I happen to enjoy punishing old-school difficulty, so if you don't, keep that in mind. The game could stand to show you a little more information regarding your score and what medal you receive on each level. Everyone beware this version though, as other people are having issues with the game loading properly. Perhaps the iPhone version would be a safer bet.
The game also features OpenFeint as well as Twitter and Facebook integration. If you can stand the difficulty, this game is definitely worth it for the retro graphics and music, as well as the fun gameplay. Check it out.