I also saw Gravity in 3D. It was indeed bright enough. I was also kind of "meh" over it. It looked fine, but personally I found the 3D effects (like screws flying at us, or the helmet visors) to be distracting. Eventually I settled in and forgot all about it.
This highlights the reason I think 3D is not impressive to most people - when they watch a movie, it *already* looks 3D to their eyes and minds, especially when the photography is excellent. I've been on a Hitchcock kick lately, and his VistaVision films all have a "3D look." The same goes for classics like Ben Hur or The Ten Commandments. At no point in those movies was I thinking "Gosh, I wish this was in 3D."
3D is a solution in search of a problem. We already perceive movies in 3D.