I've seen it twice already, in 2D and 4DX, and will probably go back and watch it again on an IMAX screen before it finishes in the cinema.
The plot is light, but is more coherent and makes a lot more sense than many other plot-heavy films I've seen recently, particularity the disappointing Avengers 2. The cinematography is outstanding, although it is based in a post-apocalyptic world it doesn't use the usual black/grey/brown filter those type of films usually use, its beautiful, bright and vibrant, and a 2 hour visual and sonic feast. I didn't think it was too long, even the second time round I was engrossed in the action from start to finish. The pacing is superb, the carnage builds to crescendo after crescendo and uses practical effects and real stunts and explosions, so the action has an impact and weight to it that you just don't get with CGI.
I can see why it took so long to produce, I thought it was better than any other action movie released in the last 10 or so years.