The biggest issue is the food. Lack of variety, and nothing was especially good. Lunch and Dinner buffets were pretty much the same things over and over all week. Fix the food, and Cancun Bay is pretty decent.
The rooms were nice. Good beds, clean, large shower. "Swim Up Bar" was next to, but separate from, the main pool. So you either had to grab a waiter, or get out of the big pool to stand in a smaller pool to get a drink. The beach area was crowded by a couple large boat docks.
Overall, if this is all you can afford, it's pretty OK. I think all six adults on the trip would have gladly paid more for better dining quality and options. I've been to two other Mexican all-inclusives, and Cancun Bay was by far the worst of the three.