Well, I'm not English but have lived in the UK and share the common European (continental lol) view on America and Americans.
I think the main reason why Europeans (yes, it's not just the English) dislike Americans are because of American politics and its impact. In my opinion, a country where the a party with values like the Republican party is so big is an awful country in my opinion. Not to mention the death penalty. The way religion integrates so much of American society is another massive problem with America in my opinion. As well as the lack of interest in other countries (excluding the Americans who actually go abroad to learn about other cultures), which I, as someone who doesn't have English as a native language, find unacceptable - Americans can even read foreign news in the own language, something I can't. However, the ways of America wouldn't really bother me if it didn't affect the rest of the world, but unfortunately it does - big time. Hence my open dislike for your country.
That said, even though America is one of the few countries I would never, ever, live in (and yes, I've visited it a number of times), I obviously realize that all Americans aren't like that and I would never treat an American badly for it. In fact, I've got plenty of American friends, both in the UK, Sweden and Germany. Obviously, if they made the effort to come over to Europe, they can't be ignorant of other cultures, and most Americans who go abroad are thankfully neither religious nor republican.