The OP question is an interesting one but a thread like this often turns into everyone simply listing bands they dont like, understand or get; which for me is a slightly different issue. A few have mentioned Queen. I too dislike Queen but don't consider them over rated just because I dont like them. Just means others have different tastes

To be over rated, I think you have to acknowledge merit in the band but not undertand the level of success or popularity they achieved.

For me, its Arctic Monkeys. I can see how they brought something a bit fresh when they emerged but the hype and press coverage they recieved was well out of proportion