I actually liked how few bosses there were. I like that they were stratified from the levels and made in their own thing. Certainly didn't disrupt the flows of the levels.
Well, there's also how I didn't enjoy most of the boss battles anyway which just made me happy I didn't have to face more. A lot of them just seemed really simple or bland.
The levels weren't as, say, intricate as the originals, but I think it's fine. The one thing they improved over the classics was that there was a stronger sense of direction, and there weren't as many springs that just inhibited movement. I really wish it were longer and had more levels though.