Nice ending, though...
... in my opionion it didn't make a whole lot of sense. Spoilers ahead.
I've read the opinion in some other thread that this movie might have been intended to have a darker ending and I'd like to second that.
Dystopian future Jackie finds out that Jack died from a head wound that he got when setting her past right? I don't think so. Or, from a different angle - why would he assume his death to be certain when on the other sie he thought he could change the future? In my opinion the movie wanders a bit aimlessly between determinism/fatalism and the possibility to radically influence the course of things.
Certainly one of the nicer time travel movies, and similar to Slaughterhouse-Five, I even liked the ending but I think it didn't fit the overall idea conveyed by the movie.
Also, all things considered, it would seem that Dr. Lorenson was shamelessly putting the blame on Dr. Becker when she said that he would have a better idea of why Jack died.
There is another interpretation: Jack originally died of a different cause and dying of a head wound again was just a coincidence. This would, however, leave the question of his original cause of death totally unanswered and would seem like a really unsatisfying ending that really didn't wrap up much. There are many details that suggest that the dystopian future and the utopian future share the same past (him coming out of the drawer and having the names of Dr Becker's victims, and a solution for Dr. Lorenson's problems).
My opinion. I would have preferred a more consistent ending to the happy ending. I think we could even have had both.