Hi Melissa!
The Ferrytale Fireworks: A Sparkling Dessert Cruise has been on my Disney bucket list for quite some time, so while I haven't personally been on it, I have read almost every review I could find. I also checked with friends who recently went on it and I couldn't find a single complaint about views being obstructed by the top level. In fact, nearly all of the reviews I read loved the experience!
The General Joe Potter ferryboat is a wonderful venue for the event. There are sweet treats and specialty drinks at stations throughout the deck. Then, right before the Magic Kingdom's fireworks are about to begin, the ferryboat will align horizontally with the park offering ample viewing space for Guests aboard.
It sounds divine and hopefully, I'll be able to add it to the completed side of my Disney bucket list soon!
Have a wonderful vacation, Melissa, and please let us know if there is anything else we are able to assist you with.
Magical Wishes,
Lauren