We did this trip in November. I thoroughly enjoyed it and although we had a bit of waiting I found it interesting and it didn't seem to be nearly as bad as the above post. I loved the swimming in the cenote but you do have to wear lifejackets so that you don't disturb the silt on the bottom 12ft down! The water is 'fresh' but do take the plunge. It is worth it. The stalactites are fab.
The buffet at the beach was delicious - we had about 90 mins at the beach - lots of time to swim and chill in the beautiful clear water and gorgeous sand. There are plenty loungers and hammocks at the beach too. I would recommend it.