It really is an amazing experience. My family has done two cruises, the first one was for Illuminations in September 2004. We left from the Boardwalk Inn and cruised around the area before parking under the bridge and watching the fireworks. We were all in awe. In March 2005 we did the Wishes cruise leaving from the Polynesian. It was my nieces 4th birthday so they had a giant cake, soda (they would have supplied alcohol as well but we declined), party hats, noise makers and they decorated the boat with balloons and a birthday banner. After touring the area we parked right outside of the castle and watched the fireworks from there. Afterwards we went and watched the electrical water parade before heading back to the Polynesian.
If you can get a cruise I would suggest taking it. You wont be disappointed!