pd1, you'll have a great time. I've been to that area three times now, and really like it. We've done a lot of different things, and I have some suggestions.
Last trip we went to Xcaret - it was terrific, an all-day adventure full of history, animals, plenty of sights and sounds, a great area by the ocean with awesome surf and sitting areas, plenty to eat and drink. A tiring day, but very much worth it.
Also, for a quieter time, but still an awesome experience, was Xel-Ha. This is a huge inland cove-like snorkeling area, and also a kind of national park. Lot of great hiking areas, wildlife, a lazy river/tubing thing with cliff jumping, lots of good food and plenty to drink. The snorkeling is terrific, it's a combo of ocean water and fresh water, it's pretty warm, and very clear, you can really see a lot of fish and stuff. A great way to spend the day, both of them.
We took a parasailing trip out of Puerto Aventuras, and also a huge catamaran trip out of that area. Kind of a neat private community, with some flavor.
For a nice evening, you can head down to Playa Del Carmen. Some GREAT food and drinking opportunities, lots of live bands and people watching, plenty of shopping. Really a nice place to spend an evening, especially with a group of people wanting to party a little.
We've been to Cozumel a couple times, really like that place. A good place to spend a day into the early evening, food, shopping, day trips, they have a great private beach there that costs some money but is all inclusive, lots of stuff to do there. But, most of it can probably be found at your all-inclusive.
A couple other notes: I found it inexpensive and easy to get around on the public transportation. They have little vans that run up and down the Riviera Maya area, that are only a couple bucks or so a pop. A great way to get around, and it's mostly just locals on them going to and from work, etc. I'm sure you can catch one close to your resort.
Those are just some "extra" ideas besides your resort, which will be good enough for most of your time already, and it's all paid for. Study up on your resort, check out TripAdvisor.com and post any questions you have. That's a great travel site, and you can really plan out your adventures by that posting board which is dedicated to travel (no competition for Jack, I don't think.).
Post any other questions you have. Sounds like you're getting some good ideas, and I'm sure you'll have a great time. Wish I was going back this year.