Ra. one can be described in two words. EPIC FAIL. If you have not watched it till now, please don't bother, remember you cannot get wasted time back. Don't be lured in by the huge hype, and marketing campaigns and promotions. The movie has literally nothing in it. If you have watched the Terminator, Iron man, Hancock, and The Dark Knight, you dont need to watch it.
Even the king Khan could not save this movie. Although the guy himself was brilliant as the nerd and super hero, but story had literally nothing.
Ra. One is like a mix of lot of things, humour, comedy, action but the mix has gone horribly wrong.
As a viewer you cannot feel for any of the three main leads when bad things happen to them. As a viewer, you are not intimidated by the bad guy's intentions and plots. You are not even thrilled by the way G. One goes off on his rescue missions. Even the sequences which are supposed to be comic just fall flat.. Plus there are a whole lot of things which felt quite stupid.
In super-hero movies it is highly important to have a devastatingly, menacing negetive lead.. (remember the Dark Knight?) which makes the movie interesting and thrilling but in this movie lacks that, among other things :)
Massive mistake in the otherwise glittering career of SRK. But you got to give him credit for trying it out and experimenting and coming out of his comfort zone.
BTW : If you have to watch it, do watch it in 3D, at least a couple of action sequences are worth watching.