UK Office was much funnier, US one is too much like a conventional sitcom for my tastes.
I love Gervais but to be honest I always found his writing partner, Stephen Merchant, funnier. I can always tell which lines are his. I think the funniest thing they ever did were the podcasts with Karl Pilkington. Very funny stuff.
The trouble with Gervais is I think he's only funny in his own context. I saw him recently in the "Comedians in Cars Getting Coffee" series with Jerry Seinfeld and he didn't make me laugh at all in that. In contrast, I found the one with Larry David very funny. They have a natural banter which eludes Gervais.
Izzard is great. Didn't he already do a gig in French though? To a French audience if I remember right.