I don't want to spoil anything but i'll just say that it's good in that it's Natalie Portman, bad in that it's super short and barely lasts more than a few seconds. But the setup is very dramatic... you'll have to watch it to know what I'm talking about.
I liked it a lot, but in a way it reminded me of a scared animal. Move too suddenly and it vanishes out of terror.
Great film, though! Sadly I had some of the quiet, intense, emotional scenes near the end almost ruined by a group of college men in the back of the theater. Oh well~
Ahhh! Magicbox, you beat me to it! :p I just saw the movie this weekend. The ending was an "interesting" TOH moment. Like you, I was also hoping they went deeper into it with Natalie Portman, kind of like they did with "Black Swan" which was full of memorable Natalie clone moments. As a lover of sci-fi, I enjoyed the film either way.