The quick summary is: don't waste your money. Don't go see it in the theater, don't rent it (even if you have NetFlix), and certainly don't buy it! The only exception to this rule that I can see is that if you see it coming up on cable and you are running into a bout of insomnia, maybe you should throw it on for a few minutes and fall asleep.
More detailed review follows if you click through:
Where Ocean's Eleven was a character-centered caper film with some cute twists, Ocean's Twelve got caught up in trying to further expand some of the character nature of the film (failing miserably) and let the caper become nothing more than an adjunct. The main devices were cheesy and given little attention.
The direction was uneven and choppy, with far too many quick-cuts, flashbacks, and strange camera angles to keep continuity flowing. And, to top it off, they used an absolutely ridiculous plot device in the final couple of sequences in the film that made it all seem not only contrived but cheap.
Even at matinee prices, I felt that we were cheated on this one... I want my two hours back.