I recommend you watch The Office UK, if you haven't already, I think the first episode is the same script word-for-word pretty much as the Pilot on The Office US. Being from the UK, I am in the minority that actually enjoys The Office US more (up until Steve Carrell left).
David Brent was such a horrible unlikable character, he really did remind me of some of the awful people you have to work with. To be honest, there's nothing more depressing for me than coming home from a bad day at the office, to watch someone else's bad day at the office, even if it is fictional.
The Office US became more of a conventional sitcom. Michael Scott is just a doofus, kind of lovable in his ways but annoying. All the characters in the US version are likeable, even Dwight.
The characters have bigger personalities and backstories, because in general American's have a different attitude and personality that British people, who are overall more cynical, sarcastic and have a miserable attitude - we'd role our eyes and complain about the cost and the noise of a patriotic parade for example, rather than having fun and being proud. There's an underlying eagerness for the American audience to support the protagonist Michael (even if he is a bit annoying) which just wouldn't work in the UK. American TV show networks also have a bad habit of flogging a dead horse and renewing a new season long after the TV show has died, so the character's had to develop to be a bit more likeable and get into more interesting and bizarre scenarios outside of the office.
Whereas the British humour is just, here is a cunt, a real-life cunt, you're not going to like this guy, he's not going to change for the sake of you rooting for him. You're going to laugh, because you know a dick like this in real life, and you don't want to see him develop as a person, you don't want to grow to like him, because he's just a complete-and-utter-cunt. It's a joke because it's a subtle satire of modern work-life. It's not trying to be wacky and have silly plot-lines.
Anyway that's my two cents on how The Office US and The Office UK haha.