The "Rivers of America" is way up on my list of favorite things at Disneyland. You don't even have to be on an attraction to enjoy it! Just watching the various watercraft go by can be a treat. I have to admit that I am usually running around the park trying to cram as much stuff into one day as time will allow. But on rare occasions I will get a chance take in the ambiance. Seeing the Mark Twain at night, lights reflecting on the water (with some gentle music in the background) is a beautiful sight.
Fantasmic has changed the river so much...I'm probably in the minority when I say that I am not that into the show. Love the dragon and the fire, but not as much as I loved the quiet riverfront at night.