Did a few segs on regional jets in august, followed immediately by a couple on an MD-80. I cannot believe I am about to say this, but the MD-80 actually felt...uh....big...after all that. And I'm 6'5". (Wow...did I really say that?) The above posts are right about the useless bin space. I wouldn't even try a rolling carry on in those...maybe just a boarding bag, and "check" your rolling carry on at the door/bottom of the stairs as you board.
It's when you spend a lot of time on MD-80's (welcome to AA) that they really do feel like goin' Greyhound with wings. You're really feel the "transition to phone booth" if connecting on one after a transpond on a 777.