It's decent, but it's not even close to the best going around right now. 30 Rock, How I Met Your Mother, and The Big Bang Theory are three that immediately spring to mind as more amusing.
Two and half men is about as amusing as arse cancer, Seinfeld was predictable and boring in every respect. I've never seen an American comedy that managed to hold my attention and actually get laughs from me, so I just dont watch them. I think I saw 20 minutes of how I met your mother. I didnt even smile. Not even slightly.
Coupling was quite funny. Top Gear is funny. Alan Partridge was funny. Blackadder was funny. Black Books was funny. Little Britain was funny for the first 5 minutes. Even Flight of the Conchords was quite amusing.
With American shows, the comedies are rarely funny, but the dramas are often dripping with real humour. House is one of the funniest shows on TV and NCIS often makes me grin (though never laugh).
Americans are often funnier when they're trying to be dramatic. But they telegraph their punchlines in comedies and I can always tell you the outcome or the punchline long before it gets there. There have been very few that haven't.
It's not that Americans arent funny either. Some of their stand up comedians are the best I've ever seen and things like South Park are f**king pissers. I wet myself watching some of those episodes. So, so wrong and so so funny.