If you don't have plans to see this movie, you can check the spoilers here and then come back.
This movie has its moments, but that's it; by that I mean that there are some pretty funny scenes here and there to book end fairly uninteresting "get the characters from one place to another" sequences and no real glue or deeper meaning driving the plot, but then again none is really advertised, so I can hardly be disappointed. Truth be told, I expected this to be a lot worse than it was, but while I wasn't blown away, I was fairly consistently entertained, so I'd say it's not a comedy classic, but a decent rental if you're bored and don't see anything else you want. I do have to say that after really getting irritated by Michael Cera the past couple years, his performance here reminded me why I was once a big fan; I really think he's at his best doing pure comedy and farce--as he is here--rather than trying to incorporate dramatic over tones beyond the grasp of that one character he plays. Jack Black is pretty effortlessly funny, but you get the sense he's just going through the motions. However, if Black is phoning it in, the impressive on paper supporting cast is mailing it in, as David Cross and Christopher Mintz-Plasse in particular are woefully disappointing in their lack of effort. The only real pleasant surprise of the whole thing is Oliver Platt, who is so committed to his ridiculous high priest character that he doesn't break it even on the DVD's gag reel. The religious stuff falls flat and the grossout humor doesn't do it for me, but Cera and Black are masters of dialogue and have great chemistry, plus some of the physical comedy hits perfectly, so I'd grade this a perfectly acceptable flick that doesn't aim for much more.