Rofl you were barking and meowing on the tambourine parts? That's hilarious. Yeah i tried singing like one song on Easy and then went straight for medium. They hold you to tighter pitch restrictions, but if you can hold a pitch anyway, i don't see how even Expert would be that rough.
Drumming is a lot of fun, but i think it's Green Grass & Hide Tides that just kills me. I understand that song is supposed to test your ability to maintain a rhythm, but cripes it never ends. Half way through my hands get beyond tired. It's funny because it's actually harder than on a real drum kit. I have to hold the sticks tighter in rock band because any bounce at all registers more than one note and that's what takes it's toll on your hands.