The Bourne Ultimatum is an easy sell. If you liked The Bourne Identity or The Bourne Supremacy, then you'll probably like Ultimatum. It is, as it should be, pretty much the same deal.
Continuing the direction of Paul Greengrass, Ultimatum is only hampered by the fact that it was being filmed as it was written and the story is much less strong than it should have been to carry such a major franchise into what will likely be its final act. Knowing this, you can easily see the seams, as the movie was constantly being written and rewritten throughout filming, to the degree that its stars never really understood what was going on, trusting that Greengrass would cobble a workable movie out of the mess.
It's not the strongest plot, but it is full-bore Bourne, definitely keeping up the action and chases but refusing to retread the same ground it's already covered with the previous movies' fights and chases. This is accomplished with a different handle on combat, a shortened car chase (inevitable after the weight of Supremacy's climax), and a chase via scooter and dirt bike. Also, kudos have to be given for the strange way in which The Bourne Supremacy's ending is reworked from a conclusion to a mid-Ultimatum plot point, giving the last film a good twist and opening up Ultimatum to be played with without being revisionists.
The one real issue that can be taken with the movie, as pointed out in interviews by Matt Damon, is that Paul Greengrass doesn't use a Steadicam. Every shot is nearly a close-up, filmed with a shoulder-mounted camera, every jolt and movement felt in a way that very few movies manage. While annoying in Lord Of The Rings, the shakey action cam (and generally shakey cam throughout) is entirely appropriate for Bourne, giving the whole movie the feel of a documentary and is consistant throughout. While it does make some of the action hard to follow, it allows for tighter fight sequences that rely less on staging and making sure the audience don't see punches being pulled and allow it to look vicerally real. The seams don't show and we feel the badassitude that Jason Bourne is supposed to give to the movie.
Despite the cloudy plot, the acting, action, and direction are all top-notch and, while some questions are left unanswered, Ultimatum gives a satisfactory close to a pitch-perfect trilogy that managed to thrill audiences without ever pandering to them.