I have not personally done one, but my best friend did one to New Zealand and Fiji. I think this was a more open-ended one without tours or anything, just had the hotels and airfare included. She had a great time and was very happy with the trip for what she paid. No complaints about the hotels or anything. I think another friend did one to somewhere in the Caribbean and was happy as well. I would be interested to hear someone's experience to a non-English speaking country as it appears those have more of the tours and guided expeditions and whatnot.
I think they're usually great prices unless you're the type to do hostels or have a lot of travel points or miles for flights and that sort of thing.