Fantasmic! is much different than Illuminations or the evening parade at the Magic Kingdom. Rather than just razzle and dazzle the crowd with how great Disney fireworks are, there is a loose story and a general storyline to Fantasmic! that someone who is not intimately familiar with the progressions can follow. Albeit, Fantasmic! is a bit over-zealous when it comes to the villains of the story. Using loud theme music to help "sell" the villains to the audience, many younger viewers may find it a bit frightening. To the rest of us, it's merely getting the idea that Mickey is in big trouble along. However, many feel that it's too big on the villains and not on the "good guys".
A major problem with Fantasmic! is due to it's immense popularity, it's tough to get a good seat. Although the Fantasmic! ampitheater holds roughly 10,000 guests, if you arrive anytime before half an hour before the show, you'll either have to settle for bad seats or not even be able to get a seat at all. To be honest, you'll need anywhere from 45 to 90 minutes to get good seats, especially during high season. Sitting in one place for that long with no entertainment just stinks. Disney has sort of addressed the problem by allowing guests who dine at the Studio's finer dining places, Mama Melrose's Ristorante, Hollywood & Vine, and the Hollywood Brown Derby, to get reserved seats with the Fantasmic! Dinner Package. However, many guests complain that the seats they get are at located the extreme ends of the theater and have a limited view.
These issues aside, Fantasmic! is a wonderful show and should not be missed. If there are multiple shows of Fantasmic! in one evening (which is the case in high seasons and during the warmer months) try for the second or third showings as they are not as heavily packed. If you're going during low season, grab a seat 45 minutes before.