Although I can see how casting the `All American' Tom Cruise would have been a hook, given the storyline, casting Jolie has probably produced a far more interesting movie and she really has excelled herself, a great performance and creation of a very memorable character. The same can be said for the rest of the cast - all generally not quite given the credit they deserve and yet they deliver time and time again.
Undoubtedly the whole project has picked up a few lessons from Bourne, good and bad, but that only serves to make a film that solidly stands on its own feet and delivers a breathtaking spectacle. No gloss, glamour or romance just full on intrigue, betrayal and combat. The story, twists and action are utterly relentless, barely stopping even when the film finishes.
Buy it or rent it. Just watch it. Salt 2 will definitely be on my `to watch' list. Can't wait.