Awesome game, buy it regardless of whether you have a PS3, and if you don't have a PS3, this is the reason to buy one.
Graphics: Absolutely best on consoles.
Gameplay: Awesome combination of perfectly tuned cover-based gunplay, platforming and puzzles.
Story: Great characters that are likeable, amazing dialogue, perfect pacing, a combination of cutscenes and in-game events making for an immersive experience.
Replay value: Multiplayer is expertly done, AMAZING maps with great designs, superbly balanced weapons, very easy to get into, a lot of fun to play and absolutely draws the player in. Co-op is absolutely addictive.
Overall the best console game this generation.
If you don't have a PS3, this is the game you should finally buy one for, if you have a PS3, you should own this game.