The problem with the jokes is that they're too broad and too simple that they just don't hit the right notes. I'm surprised Ramis (and co-writers Gene Stupnitsky and Lee Eisenberg, both of the U.S. version of The Office) actually thought this stuff was funny, let alone passed it with personal approval through the scripting stage. The attempts at satire on religion, and more specifically the Bible, are lost when it reverts back to silly slapstick or racy innuendos. The ingredients are all there for a good, solid comedy, but the chef with the name tag that read Ramis doesn't seem to know what to do with them.
Even the plethora of comedy-actor cameos can't even save Year One. I can't believe the amount of normally funny folk was brought together in one place here, and find it even harder to believe it was even possible to misuse them so drastically. Paul Rudd and David Cross (both hilarious guys in almost everything else) play brothers Cain and Abel (you may have heard of them), and a scene of them squabbling in a field, for example, feels watered down for the kiddies - if this were Judd Apatow's movie (he produces but doesn't write or direct), he'd really have them go at it. Superbad's McLovin, aka Christopher Mintz-Plasse, seems just to be in there because of his famous geek role, and a normally brilliant Oliver Platt is just embarrassing, providing a gross-out comedy moment involving chest hair and oil that's beyond unfunny. Even a playing-it-straight-Vinnie Jones is utterly wasted here.
For the kids in the audience there's the obligatory fart and poop jokes (the latter sees Black shockingly chewing on what turns out to be bear poop - can someone explain to me why that's funny?), and the slapstick violence (one area where the film manages to stave off questions of explicitness for the age rating). For the adults there's some moments of well timed punchlines, the occasional smart commentary on religious traditions (one of the film's highlights is a scene where they debate the point of having your foreskin removed), and the general "spot the comedy actor" routine. Perhaps it's not a coincidence that Year One shares with Night at the Museum 2 the description of "meh" at so many points, but both have their absolute highlights coming from Hank Azaria's appearances. Unfortunately, as he was during his night at the Smithsonian Museum, Azaria's screen time is disappointingly short-lived here.