Legacy was perhaps a completely unnecessary sequel, but I actually enjoyed it nonetheless. Jeremy Renner made a good "Bourne", and had Matt Damon not been available, then Renner would have been a pretty good choice for the original trilogy. Rachel Weisz was as alright as usual, playing a similar character to Evy in The Mummy but rather more capable. There was some attempt to give a reason for why the "assets" are as bad-ass as they are. Now I am usually one of the first to complain about "Spacker Science" in films, but I thought that the claims they made (however implausible) made sense within the scope of the film. It is certainly nowhere near Midichlorian territory!
Impressive action scenes and solid performances from many respected actors including Edward Norton and Albert Finney make Legacy an enjoyable younger brother to the Bourne series. Fun and exciting, but lacking the impact of the original.