Not challenges, only collectibles.

What's your settings? My laptop has a 5870m which is far more powerful but i can only play it on low at 1280x720 with FXAA!

You should be fine at recommended settings!

like the game, but it could have been better optimized, anyway a solid 8 is the least it deserves.

You should be able to run it on Medium. The engine for this game is quite poorly optimized i think.