Well, saw it yesterday afternoon and here's my semi spoiler free review:
Not as good as the first two, but still enjoyable. Definitely a lot of laugh out loud moments and gross out humor. Stiffler definitely steals the show. And the dead weight characters - Vicky, Heather, and Jessica - don't show up and if you think about it, their absence really doesn't need an explanation. I would have liked an explanation on why Oz wasn't in the movie, but his absence doesn't really bother me. He's one of my least favorite characters. Nadia doesn't show up, but does get a few mentions.
And I have to say this about Fred Willard and Eugene Levy - comedic geniuses. IMO, FW stole the show in Best in Show and Waiting for Guffman and in the few scenes he was in in AW were hilarious - the bachelor party scene is the first to come to mind. EL as Jim's dad, funny as always.
And Michelle's sister. Definitely