We've eaten dinner at Chef Mickey's twice (including this past Thanksgiving) and enjoyed it both times. It's not cheap, with T-Giving dinner for two adults and two kids (including a couple of beers) running up to about $100 with tip. I can't remember if it was more expensive for Thanksgiving or not.
The buffet is good and has a wide range of choices, including a carving station with prime rib and other goodies. There's also a kids' section with pizza, chicken strips, etc.
Characterwise, they usually have one serving as a greeter (I think it was Donald the last time we were there). Other characters, including Goofy, Mickey, Minnie, Chip and Dale, circulate around to each table to pose for pictures and sign autographs. You'll get the full crew by your table during a normal dinner time. They also do a napkin twirling thing from time to time.