I really enjoyed NRJ, as did I the whole Pandora area. It's a relaxing, immersive experience with lots of eye candy. I don't think it's fair to call it filler or a diversion as it's an experience, albeit brief, that stands on its own.
I like how the screens are incorporated into the physical scenery and have multiple layers for depth. And the Avatar musical theme builds through the attraction , culminating in that breathtaking AA, which is very effective.
That being said, my main critique is pretty similar to everyone else's: it needs more physical animals/Na'vi. For example, the first Na'vi sentinel at the beginning; he stands still and just says a few words. There is no reason he couldn't have been a limited movement AA. In the stretch between the overhead leaves and the scenes of the Na'vi processional, there's really only 2 animal sitings (the centipedes crawling and those deer things) and they're both projections. This would have been a perfect spot for a physical animal, maybe a head of one of those hammerhead rhinos poking out from the forest and drinking from the river.
I also agree with most this could have really used at least one additional scene. I believe the whole point of this attraction is to demonstrate the Na'vi's spirituality and connection with the Flora and Fauna; if that's the case, I think it's a big misstep to not feature a scene with the Tree of Voices or Souls. Not only would it have a visually-impressive set piece, but it's a major element of their faith to not demonstrate.
My only other observation is that the land as a whole does an amazing job of setting a theme and story of the ecosystem starting to recover from RDA's destruction by showing company equipment being repurposed and structures crumbling and being reclaimed by nature. I believe it's implied the NRJ takes place in a former mining site, but it doesn't look like they fully-followed the themeing to communicate that in the queue or loading platform. I think they really could have used more mining equipment strewn about.
A few changes and I think this could have been a solid D ticket, A Grade attraction. As it stands I agree with the C ticket designation and would grade it as a B or B+. Definitely will re-ride it if it has a minimal wait or need to get out of the elements).