Anyway the first three makes a great trilogy, but I saw no reason why they couldn't keep going with the right story. Bourne Legacy has all the trademarks of being that story, but it doesn't have enough panache to pull it off.
The long version is of course spoilery. That's your warning.
The first missed opportunity was the fact that by missing his dosages of the blue tablets Aaron Cross was slowly losing his mind. The film sets it up only for it to happen just as they get to the facility to conduct the viral procedure to bypass it. It's a threat that's never gone through with. It would also put Rachel Weisz's character, Dr. Marta Shearing, in a position of standing up for herself. Cross guides her through everything, what would have happened if he hadn't been in a fit state to do that?
My personal preference is that his mind is gone after the plane journey, leaving the whole of Manila for Dr Shearing to stumble through herself. A lesser variation of it would be during the viral procedure itself. Here they are interrupted by security guards after it is too late, the procedure is already done. What if it was still cooking and Cross had to buy them time, all the while still losing his faculties? Put more tension on the scene then 'Will he win this fight?' Of course he will, he's
BourneCross. After making such a big deal of him losing
his mind we never really get to see it. If they intended it to be a
ticking clock, that failed too. There's just a moment of him starring
into nowhere and another of him losing track of what's going on.
Not happy having Cross slowly descend in mental anguish (it could be a little heavy for summer blockbuster)? What about when he's out of action due to the fever the viral solution causes. In the film his head completely clears just as the police turn up. Well isn't that convenient. How much better would it be if he was still fighting the infection instead? You could even play off the angle of Dr. Shearing standing up and being counted again instead of just being really good at shouting. Maybe even break up that massive chase sequence into two, one with the police with Cross out of it, and a second with him back in it against the other agent.
I'm not saying all of these were needed but something certainly was, just to make the film stand up on its own. In fact if they went with problem 1 or 3 I wouldn't bother with the other since the drama comes from him being out of action and both deliver that. 1 also discloses 2 as 1 requires him to be out of action, while 2 is him struggling.
While we're on the subject, what was up with the bloody camera work? It was my problem with Mission Impossible 3, it is my problem with Bourne 4. I can't see a fucking thing that's going on. The stunt of grinding the motorbike down a crowded staircase was completely ruined. We even know there's a decent shot of it because we saw it in every sodding trailer there was.
But camera work is a minor niggle compared to its lack of real tension. Bourne Legacy is seriously suffering from middle child syndrome, something usually associated with second films.