So you could potentially only spend a couple hours in the Rock and Roll Hall of Fame and still be satisfied that you saw everything. But if you wanted, you could spend the whole day watching videos that they play.
There are some pretty interesting exhibits, mostly on the bottom floor and even the special exhibit. But the in between floors seem more of just fillers than actual interesting exhibits. I'm not really sure that the museum is worth the $22 they charge. Even the Lourve charges less than that and there's a lot more stuff to see at the Lourve.
It's worth seeing once, but not so sure that I'd pay that much to go again.