The BBQ gets pretty poor reviews around here, mostly because it is 2 TS credits for picnic food. We've gone a few times and we've always had fun. If you have little ones that are at an age where they would be excited to dance with Mickey and the gang, I say give it a try. Just keep a few things in mind...
It is outside under a pavillion so heat/rain may be an issue. From what I've heard so may the bugs on the really hot days, though I have not had that problem personally.
The dance floor gets crowded and a few people can be a little obnoxious pushing their kid in front of yours to dance with the characters. (If you've ever been to the "dance parties" during the Halloween or Christmas Party, its kind of like that)
It's picnic food - burgers, hot dogs, ribs, salad, watermelon, ice cream, lemonade. It's not great, but its fine. Beer and wine are also included if you so desire. I did not leave hungry, but it certainly was not my best Disney meal.
Seating is first come first served, so get there EARLY. Like at least 45 minutes early. Shoot for one of the tables facing sideways along the dance floor. The tables are looooong picnic benches that you will be sharing with others. Good if you're the type that chats with everyone. Not good if the person you're trying to chat with is not.
Most of the bad reviews I've read came from people that didn't know what to expect. They booked a dinner show called "Mickey's Backyard BBQ" and complained that the menu was burgers and hot dogs. There is dancing with the characters and they complain that the place is full of kids. It clearly tells you that it is an outside pavillion, but they complain about the weather.
I say give it a try. My son is 4 and we've gone a few times and always enjoyed it. When the characters are taking a break, the country western band still plays and there's other entertainment.