Does everything the previous game did, for good and for worse
Gameplay: This will be pretty short: The game feels largely the same since last time. There are some new mechanics and weapons, but if you really enjoyed the actual gameplay from the 2nd game, you'll like this. One thing that made the previous game much better IMO is the blind fire mode. In the previous game, it was much more useful. Here, you hit almost nothing. While realistic, for those of us who don't like aiming with a PS3 controller, it's not good. If you don't mind doing then, then basically disregard that, as you'll enjoy it.
Platforming is the same as before.
Puzzles are pretty well done, and some have a nice scale to them and make you think but nothing revolutionary.
Sound: I'll say again this series has to be the best acted(note I did not say voice acted) ever. It truly feels like an interactive movie. Little nuances really make the characters feel alive.
While there are better 'voice acted' games, this series, again, is the best overall acted.
The score is great. I love Nate's Theme. The music is good but not amazing. Gives a good sense of mood but for better or worse, feels like a generic action movie score.
Atmosphere/Environments: This is where the game really improves over the last. While the last game had varied environments, I didn't really prefer many of them. This game does an AMAZING job with it's environments. They feel real, gritty, and alive. And varied. My goodness this game has everything from crowded middle eastern cities to lush jungles, to barren deserts, and of course caves/caverns to explore.
Story: While the series has never been totally story driven, in the sense that there are 100 twists and turns and swerves, plot twists etc, the story in the last one kept me really engrossed. The interaction between Nate and Elana in the last felt real and completely draws you in.
*****Minor Spoiler*****
The character Elana returns, not surprisingly, but her interaction with Nate was not nearly as interesting.
****End of Spoiler*****
Sully, on the other hand, is wonderful in this game. He's not dropping G Dammits every 5 seconds and feels more real and likable, while still maintaining his classic quasi-pessimism. In short, he's a much more 3-dimesional character.
The main enemy is better than the last game. She too feels more 3-dimensional.
Conclusion: If you liked the previous game, this one does more of the same. It does game a few gameplay upgrades but not nearly enough to make it feel fresh. While the environments are 10x better this time, the story that takes you through them is is not quite as good.
Fittingly, I saved my thoughts on the ending til, well, the end of my review. The end(or near end) of the 2nd game kept growing and growing til you though "Oh my gosh, you mean that wasn't the end....awesome!" . Thought the actual final boss fight was a bit lacking, the build up to it was possibly the best ever. This game's ending ends rather abruptly and the final boss fight lacks any sense of scale or importance. Once over, you're left feeling "Wait, that was the final fight, there's no more?".
To sum up. Good game, improves in a few areas, but overall, I preferred the 2nd game. That could be my utter disdain for console aiming systems tho, so it you are a console fps vet who really likes that sort of gameplay, you'll likely enjoy the actual gameplay more than I did.