We stayed there last year and thought it was very nice. This year we stayed at Horizons by Marriott and preferred their decor...more casual and beachy whereas Mystic Dunes is more formal with leather couches. We had asked for a unit by the new pool, which we were granted. Unfortunately when our "hostess" led us to our room, the new pool was not open and she commented that it wouldn't be for another month or so!!! She was very helpful though, went into the condo and called the office to switch us to a different building near the main pool.
The kids enjoyed the pools and the mini golf. As I recall there was free breakfast, but we needed to have a quick bowl of cereal to get to the parks when they opened, so we just ate in our unit.
We liked the layout of our two bedroom unit, as the two bedrooms were on opposite ends of the condo. One, with two queens I believe, for the kids, and one with a king for us. Also a nice big tub in the master, and a screened porch off of the living room which was really nice.
Complex is convenient to parks, particularly Animal Kingdom.
Mystic Dunes just changed its name from Wyndham Palms, so if you do a search on that you might find more info. Jeanne B on the DIS was an owner there when we went and she provided a lot of helpful info if you can find any of her posts.