I've seen Fantasmic! multiple times and I do love it, but we have skipped it the past few times.
The problems with it are this, for us:
-dining options at DHS....as in, there aren't any that we are interested in so we'd have to eat somewhere else early and then hoof it over to DHS
-crowded, crowded...there is always a line early to get into the theater and then you have to sit and wait on stone benches for an hour before the show starts
-"black clouds of death"...it never fails, when we schedule F!, we get to DHS and the black storm clouds come rolling in. We've had downpours, lightening, etc that has ended up cancelling F! after we had been waiting for a long time.
This sounds like me... now, we have only seen it once, and while I really did enjoy the show, I didn't enjoy the after the show. EVERYONE heading towards the exits/buses in a torrential pour down of rain, getting crabby because my shoes/socks were soaked, 2 kids who were tired and wet, and 1 husband who wasn't being the most patient about it. We skipped Fantasmic on our last trip and just enjoyed the park while everyone else was @ the show.