If you can stand to read another one about Coz, read on. We go just about every year. We just completed trip #20 or 21 this past May (losing count now). Coz is the best bang for your buck in the Caribbean without a doubt. The diving is outstanding, the people are nice, the atmosphere is laid back. Best dive sites:
Palancar Gardens, Palancar Caves, Santa Rosa Wall, Columbia, Punta Sur, Punta Dalila, Punta Tunich. There is no bad dive in Cozumel. Tormentos, and Yucab are coming back from Wilma - they wer hit pretty hard, but even so, still a good dive.
We saw a giant loggerhead turtle at Columbia this past May; about 5 feet long.
Your hotel has good access to the dive sites and they use fast boats. You will be within walking distance from town (about 15 minutes) or a cheap $3 cab ride. You don't need to rent a car in Coz for more than a day to do the island tour. Otherwise cabs are plentiful and cheap. Make sure you go to town square on Sunday night; the locals usually have a little fiesta and it's great to walk around and enjoy the sights and sounds of Cozumel. Great restaurants - Capi Navigante,
Pepe's (best beef on the island a little pricey but worth it), Sonora Grill, La Choza, La Mission, try even the cafe's in town square - Cafe Denis (lunch), Las Palmas (breakfast), Prima. Tulum is a good day trip and will cost a few bucks but it is worth it...(but do you really want to leave Cozumel once you're there?) You can go to the San Gervasio ruins on Coz in the afternoon after diving and have a look -cheaper and you still get culture or go to Cedral in the afternoon. Cabs will take you to both places. Have fun! You may find that you'll want to come back every year.