We heard many of the same comments from our guests, especially about their wanting to make a vacation out of attending the wedding. My daughter was married south of Cancun at the Fairmont Mayakoba, and our guests were very happy with the resort. They told us they would have picked the location for their own vacations, and some said they were coming back! Two bought time shares in the area (!). and many stayed beyond the days that included the wedding events.
The Fairmont development is a bit isolated, but our guests seemed to enjoy that feature. The food was fabulous, the beach and pools were lovely, and the eco-firendly grounds were gorgeous. A taxi into Playa del Carmen was less than $20, and several of our guests spent at least one evening there, although most were quite happy spending their time at the Fairmont. The services offered by the Fairmont's events office allowed us to avoid the cost of a wedding planner or travel agency, and we contracted with local vendors for the decor, ceremony and entertainment. Let me know if you want for info.
A good reason for selecting the Riviera Maya for a wedding site is that flights into Cancun are generally inexpensive, and flight times are reasonable from just about anywhere in the US. Don't be put off by online room rates as your guests will receive a reduced block rate as attendees for your wedding. Contact the events offices at the resorts you like and see what you can negotiate, including extending the rate beyond the usual day before to night after package. A good place for searching various locations is under the hotel reviews on tripadvisor.com. Search your city/region, and there is usually a live map that will show you the locations for the resorts reviewed on the site. These won't be wedding reviews, but you can learn more about the resorts.