I actually thought the movie was pretty good.... although I'll definitely be sticking with standard 24fps for the next two.
The 48fps was certainly interesting to experience-- and it really did make the 3D feel as natural and smooth as I've ever felt it-- but ultimately it just removed too much of the magic from the screen for my taste. Instead of feeling like I was getting a glimpse into some other, wondrous world, like in LOTR, here it felt most of the time like I was simply watching actors on a movie set. Or like I was watching the most expensive home movie ever made.
It also had the odd effect of making even the natural scenery look a bit fake. The trees and mountains that passed under us looked as much like models as Rivendell did, which was weird. Although unlike others here, I had no problem with the CGI. I thought most of it was integrated pretty well, and looked fantastic.
The story did drag in a few places (particularly in the beginning), but no more so than in LOTR. And the action wasn't nearly as cartoony or over the top as I had heard it would be either.
Ultimately, I'd probably have to give it a B. Although I suspect that'll go up once I see it in 24fps.
(Oh yeah, the Trek and Man of Steel trailers also looked freakin fantastic as well)