A Round-up of some RoL reviews. Certainly not anything stellar:
"Overall, this is NOT a nightcap to your day at Animal Kingdom. We’re still not 100% sure on calling it a nighttime spectacular, but it’s definitely something… just not sure if that something warranted a seven month delay. We went in with low expectations and were blown away by the technology used, but were left wanting more by the finale... This belongs at Sea World as of right now, not at Disney’s Animal Kingdom." - WDWNT
"Overall, the show (in its current form) has the ability to underwhelm guests. It will be a beautiful thing to watch, but will have no lasting effect or payoff for the guest. I hope that what we saw tonight wasn’t the finished product, or if it is, Disney continues to work on a version 2.0 of the show immediately." - Blog Mickey
"Based on tonight’s preview, it is clear that Rivers of Light is something special, and very different from the other Walt Disney World nighttime shows. It’s closest relative would be Reflections of Earth, but it is of course not a firework show. Perhaps the biggest criticism we have from the preview, is that there isn't a real sense of finale or conclusion. Somewhat like a song that fades out, the show concludes in a way that might leave some wanting more." - WDW Magic
According to WDW Magic, the show is 18 minutes in length.