It's a cute little ride. It's a nice addition for the younger set, especially considering that the majority of Epcot's attractions are geared towards older kids or adults.I think more could have been done with it though. It's slightly above a Fantasyland dark ride and with those expectations its a nice little ride and is certainly better than the old sea cab ride or no ride at all. I wouldn't wait more than 20 minutes for it though. I don't know if they frown on this or not, but if the line is long, at least now you can enter the rest of the pavilion now through the automatic doors at the exit area.
That said, for a truly outstanding Nemo themed attraction, check out the new Finding Nemo-The Musical at AK. It is, imho, the best live show on property at this point. It is simply spectacular and if it were longer and had a few more extravagant sets, it could easily be transplanted to Broadway, it is that well done. The performers do an excellent job with this one and have great NEW songs (afterall, Nemo, the movie, wasn't a musical, but you might have wished it was after seeing the show), costumes and material to work with.