Two years ago I went to Copamarina in Guanica, on the SW coast.
www.copamarina.com We got a great deal for a 5 day trip. The dive op was a bit of a screw up with poor management and inbetween captains so we didn't get in all the diving we booked. (If I ever go back I'd dive with La Paguera Divers and not Dive Copamarina.) The dives we did do were nice. They've only recently implemented the use of bouys rather then anchoring boats and there have been no real fishing regulations so the marine life was not that diverse or overly abundant. The walls were easy dives and nice with lots of fans and coral. Shallower reefs were ok. It' won't come close to what you've seen in Cozumel but if you go without any big expectations you'll enjoy it.
The resort was very nice and we liked it. We had an AI plan it was well worth it as it's not really close to many restaurants and the menu prices were $$.
There's other interesting stuff in the area - the bioluminescent bay, dry forest, very scenic drives along the coast and through the mountains.
Overall, if it's a great deal that you can't beat then go and have fun. If it's close to what you can get for the same time in Cozumel, Caymans, Turks & Caicos, Curacao... then skip it and pick a destination with better diving.