Just one word of advice Bullseye....the first half of the first season (american version) is basically a word for word copy of the BBC version which really annoyed me. And since you are a fan of the BBC version it will probably annoy you as well.But stick with it because once they run out of material to steal the show actually gets really really funny, right up there with the BBC version on some levels.
Casting-wise, the BBC version has a much better cast with the exception of a few roles (Jim and the temp). But that said, the American cast is still great...just not as great as the BBC version. Steven Carrol does a great job, but he pales in comparison to Ricky Gervaise (who btw is a producer of the American version). Dwight, who plays Carrols right hand man is great, but as great as he is he isn't half as good as what's his name, the really skinny guy with blond hair on the BBC version.
The support characters on the american version might be better than the bbc version though.