I once wrote a small dissertation on the differences between the original and American version of The Office. Unfortunately, I lost it after an unfortunate system crash, and could never muster the enthusiasm to rewrite it...
Fortunately, John Phillips over at Off The Telly seems to have comparable thoughts to my own, so I recommend you read his excellent, well-reasoned comparison here.
To summarise my own thoughts on The US Office, in a paragraph: I really like what they're doing with Jim/Pam, appreciate the wise decision for Michael to not be a Brent clone, I think their expanded cast works quite well, I generally hate the amount of times they leave the office (as it's usually forced and unlikely), I detest Dwight (a misfiring one-dimensional cartoon), I cringe at the sillier moments they shoehorn into scripts, and it bugs me when the conceit of a documentary crew filming them for TV is blatantly ignored – and it just becomes a "filming style".
Fortunately, John Phillips over at Off The Telly seems to have comparable thoughts to my own, so I recommend you read his excellent, well-reasoned comparison here.
To summarise my own thoughts on The US Office, in a paragraph: I really like what they're doing with Jim/Pam, appreciate the wise decision for Michael to not be a Brent clone, I think their expanded cast works quite well, I generally hate the amount of times they leave the office (as it's usually forced and unlikely), I detest Dwight (a misfiring one-dimensional cartoon), I cringe at the sillier moments they shoehorn into scripts, and it bugs me when the conceit of a documentary crew filming them for TV is blatantly ignored – and it just becomes a "filming style".