Its great. I love the free roaming element and the way you can jump building to building, the way he climbs them is also incredible. There are also tons of great mosques and Churches that you can climb trully breathtaking.
The setting is also incredible (crusades) one of the reasons why i bought it. the story is also great although there are stupid elemts to it.
When i finished the game it felt hollow (like san andreas) but thats with many games, but overall a great gaming experience that shouldnt be missed.
I've also got COD4 which is easily the best FPS on PS3 IMO. Although the campagin is short but its still fun.