I've been to Cozumel and I enjoyed my time there. The weather was terrific and there's lots of interesting shops. With that being said, there are some agressive salespeople and though there are interesting things, it isn't really bargain city.
Some of the bars have happy hour (2 for 1) and provide for nice beachside relaxation. I know there are also multitudes of excursions, and if you've got lots of time there you can even go as far as the Mayan Ruins.