You have to take in to account that american networks pump ridiculous amounts of money in to their shows, amounts that the likes of the BBC could only dream of.
No British tv company has the money to make a Game of Thrones(though lets face it, that may as well be a british show) or a Boardwalk Empire.
Most of our dramas are absolute trash tbh, but again, lack of funding etc
Sherlock is pretty awesome though, and can stand up against anything on US tv imo.
Comedy wise we are extremely hit and miss. For every office there's 2/3 mrs browns boys/mirandas
Same with US shows really, they produce so many shows they're bound to get it right now and again, and even when they do, they more often than not find a way to mess it up.