Good film, but not quite worthy of all the 5 star praise it's getting IMHO. Interesting story, but as with any sci-fi I guess you're going to get a lot of "why didn't he just do X?" - which is what I heard a bit of when leaving the screening.
Also to be a bit of a pedant, if you're going to use prosthetics or whatever to make JGL look like Willis, why not do his ears too. Totally different shape