I've been to Cancun. Very resort based.
I love Playa Del Carman just south of there.
I love exploring and doing things on my own, I'm not a fan of the resort based things where, "Tomorrow at 10am be out front of the resort and the bus will take you into town to go shopping, or take you to these ruins and on the wayback we'll stop at two overpriced junk shops so you can buy cheap trinkets.
Playa Del Carman is very European, late night dinners in open air cafes, small open air bars on the beach w/ wooden dance floors and local bands.
I just find it the resort thing at Cancun weird, you eat all of your meals there, you hang only with other tourists, you have dudes w/ mics running around the pools trying to get drunk tourists to play drinking games.
One trip down there my buddy and I signed up with a college archeology tour out of the back of Archeology Magazine, very cool. There are some amazing ruins around there and we got private tours to all of them. We stayed in a really nice resort in Playa Del Carmen while everyone else stayed at some hostel.
If you don't like Mexicans stay in Cancun, if you want to learn some history and culture stay in Playa Del Carmen.