I think the first thing that strikes you when you see this movie is the level of emotion on display. The earlier movies had a certain cool reserve that masked whatever emotion the main characters were feeling. This one dared to be sentimental. Not that I think this is a bad thing, mind you.
However, the movie does have its share of problems. First of which is Al Pacino. In the first movie, Andy Garcia conveyed a sense of menace - you felt that he could, and readily would, hurt these guys. In the second one, Vincent Cassel conveyed the sense that he was competent enough to beat these guys. Although with the trick ending right at the end, it was difficult to tell whether he really was. In this one, however, Al Pacino seems to be filling in for the villain that the makers thought Al Pacino could play. He displays less than a tenth of the energy the character needs to have, and less than a hundredth of what he could. However, not all the blame for this performance can be laid at his door. His character is written as someone who is supposed to be quite smart, but the script never really bothers to demonstrate it.
The thing is, intelligence doesn't work the same way as evil in the movies. You could merely hint at the evil a character is capable of and not really show it except in the occasional instance, and people would fill in the blanks for themselves. But with intelligence, you need to demonstrate that the guy is smarter than the people around him - if you don't do that, you can't make people invest in the hero's success. If there was no-one of Lex Luthor's calibre, would you feel happy when Superman won?
The second problem is the payoff. The movie has a sort of kind, gentle tone throughout the elaborate process of setting up the con, which would've been okay if it really managed to deliver a zinger of an ending. But the movie prefers to play it straight, and just brings up a few small surprises, none of which are really surprising to anyone who has watched the two earlier movies closely enough. Maybe it's a problem of expectations, but that's a burden that any third installment in a series would doubtless carry.
The third problem is the humor. The material is so obvious, it's almost juvenile. The Ellen Barkin character, for instance, is written and played too broadly. As is the entire segment in the Mexican factory. You get humor when you're looking for wit. The movie does have the occasional laugh-out-loud moment that really hits the spot. But these are too few and far between.
Let it not be said that this review is one-sided. The movie does have some good things going for it. For one, it's not boring - there's the pleasure of seeing an elaborate con being set up. Then there's the pleasure of watching a bunch of talented actors who have grown comfortable with each other over three outings. And then there's the pleasure of watching George Clooney and Brad Pitt interact with each other. Danny and Rusty have so much history together that their communication has by now become some kind of code. They speak in half sentences and faint gestures, and yet it manages to work.
Clooney is a master at conveying volumes while not moving a single facial muscle, and Pitt has always been a great comedian (I thought he was dynamite in The Mexican, although James Gandolfini hogged all the glory). Watching them react to Linus' (Matt Damon) earnest statements is a master class in how to evoke laughter with the barest minimum of effort.
However, on the whole, this is yet another in a series of disappointing third acts that we've been subjected to this year. Especially so because so many of these series had fantastic second outings. I remember telling my wife that it seemed like the Sophomore Jinx was now a thing of the past. To paraphrase the promos of Ocean's Twelve, it looks like three is the new two.