I just returned from our cruise on the Star (Jan 4-12) and we DID the Manzanillo Resort Getaway. It was Resort Real (pronounded "ree-al"), which is an all-inclusive resort. The buffet was included as well as an open bar...all day. The pool was nice and there is a swim up bar - stay away from the watered down mixed drinks and stick with beer and tequilla shots. ;-)
The beach was not particualarly nice, with cloudy, somewhat rough waters and a very strong tide. We rented snorkels from the hotel for $15 US but gave up the snorkeling &beach area after about 45 minutes of have out butts dragged up onto to shore with the waves.
We were dissapointed in the beach, but at least we definately got our money's worth out of the open bar. Honestly, given the opportunity, I wouldn't book this excursion again.