Uncharted 3 is a beautiful game and fun to play, but it isn't perfect
Warning: spoilers to follow
However, there were some downsides. While the voice acting was good the characters weren't as great. You have a new partner in crime but apart from the fact he is helping you you know nothing about him, the return of Chloe offers nothing new for the character and they both bail out half way through. Elena appears and apparently her and Drake were married/still married but separated between the games. The game doesn't try to look into it (though it isn't surprising since Drake tends to go off and piss off international criminal cartels, it can't be good for a stable happy marriage) or use the potential of the situation for much. You get to see how Nathan met Sully and there is a genuinely OMG moment with him when you reach the lost city. The bad guys are all mysterious, but nothing is really made of them either.
The story is also pretty average. It is what you expect of these games: a search for a lost city and the treasure within. The story is confusing, particularly in the reasons why the bad guys are doing what they are doing and how much they apparently know. A good thing they did is avoid the monsters in the lost city cliche from the last games (or at least side-stepped it). However, unlike the previous games the major treasure/curse is not explained at all. The game also made use of several sections where all you do is walk/run where there are no enemies or platforming, which are nice breaks in the flow, but they do get boring because they last a bit longer than they should. They probably would have been better to be purely cinematic as actually having control of Drake is meaningless.
These faults hold back the game from perfection and in my opinion drop it down below the quality of the second game. However, the game is overall a fun experience and if you're a fan of the series it is still worth the time to play.