My husband and I spent a week in Casa de Campo this past March. It was awesome! Service is great, the grounds are gorgeous, and the various restaurants are very good.
The beach is not great as compared to other Carribean destinations (i.e. the water is not crystal clear and the sand is not white, but just light brown).
The day trip to Catalina Island sucks. I would not waste my time doing that. The snorkeling is no good and if you lay on the beach you will be tormented by old ladies trying to sell you ugly necklaces. The beach is pretty though if that's what you must have.
If you have any other questions, let me know. - Shelley