Just did the H&V Fantasmic dinner earlier this week (tuesday night) and I was pretty happy with the whole thing overall. Far and away the best part was getting in and OUT much, much faster than without the special ticket. The seating for the show is great, also.
I don't know if I'd want to do a birthday dinner there, though, it is kind of utilitarian, doesn't have a lot of the 'disney magic' going on. I'd pick one that has waiters that are more into the whole serving thing for a better birthday experience-the waiters at H&V are mostly about replacing drinks and clearing plates, not a lot of interaction. It's more about the eating than the experience there, so you may not get the 'everyone sings happy birthday' thing because everyone's intent on loading up and then heading off to Fantasmic.
You can get kid's stuff for the grownups-we got the plain steamed broccoli for us, and I saw a lot of people somewhat sheepishly bending extra low to scoop out the mac and cheese (the kid's buffet's in the middle where the two buffet lines meet).
The food's not amazing, but it's not horrible, either. I'd say decent. There's a pretty good variety. I was pretty full when we left. I think the desserts are kinda mediocre, though. Crystal Palace's desserts whoop butt on H&V's. Tiny sort of tart thingies, a little stale tasting.
We had a 6 pm ressie and we got to watch the Stars and Cars parade just before we went in and saw Darth Vader walking behind Luke and Leia on a landspeeder. Too cool!