I went to the Halloween one last year. IMHO the food was OK, not great. I would have really liked pumpkin ravioli as the previous poster mentioned was at the December one, but didn't find this in the Halloween version last year. It was worth it more to get pictures of the characters in their seasonal costumes, for example the picture in my current avatar. I think they added these characters and seasonal costume changes because they weren't getting enough business based just on the food. This was a smart marketing idea but it would be even better if they would also improve the food quality. Nothing was bad; I just didn't think it was great.
I didn't notice any solo diners at this one, but there might be some at other times, don't know. For what it's worth, the families are usually so focused on themselves that they won't even notice you're there by yourself. I've gone solo to other character meals but prefer company for these, as it's helpful to have someone there to take your picture, in case the server is too busy and the character handler is elsewhere, as sometimes happens.