I can't comment on the balcony seating, but last week I did the riverside seating (first time), and I thought it was great! I was hoping the desserts would be a little more substantial (they did have the chocolate covered strawberries though), but I really booked it for the reserved seating more than the desserts.
I originally wanted balcony, but the seats were sold out. I was kind of glad I got riverside after reading some of the posts that mentioned blocked views.
If you get riverside, this is what my experience was like:
The show was at 9:00 p.m. We checked in at about 8:10 (even though guest services said to check in at 8:30). It was a good thing we did, because 6 other parties were already there, and they seat in order of check in. At check in, they gave us a number, so we were party #7. They told us to come back at about 8:30, but we just hung around. Just before 8:30, they took "attendance," making sure all of the parties were there. Then, they started seating parties one by one, in order of check in. We had a "substitute" person escorting us (her choice of words -- I guess she doesn't normally work at Fantasmic, but we thought she was great). She even allowed us to choose from several different seats, pointing out the pros and cons of each area.
Once we were seated, someone took our drink orders, and we were able to help ourselves to desserts. The server came to check on us a couple of times to see if we needed more drinks. For the desserts, there were chocolate covered strawberries, Mickey-shaped rice krispie treats, a raspberry filled cookie, biscotti, and macaroons. There might have been a couple more choices, but that's all I can remember. I was kind of hoping there would be a few more choices, like maybe cakes or pies, but for me, just having the reserved seating was worth it. We stuck around to watch the fireworks afterward, and we thought it was a great viewing spot.