Yeah, I remember watching the movie with my dad and my brother back in 2007 after it won the Oscar, and we got that same feel of disappointment when it ended..
Yet, two years ago or so I decided to give it a second try, because a guy recommended it to me, and even when I told him that I didn't like it, he said that I should watch it again and pay more attention.. Besides, I knew that when I first saw it I was a teenager without the experience I had now after seeing lots of movies and the like, so I did it..
That second time I happen to liked it much more, although most of that was because right after finish watching it I found a few explanations on some pages that matched what I noted while watching it and other that went beyond.. There were some details that I had not noticed, and the more interesting theories about the meaning of the film fit all those details.. Explanations I saw are in the vein of what Kotowboy and KevShmev have said..
Predestination. There is obvious time paradox but I guess movies is built on that. Very enjoyable nevertheless, Hawke is amazing.
I read the short story the movie was based (before watching the movie), and it was one of the best things I've read.. I'll say is a MUST READ.. Short story, by Robert Heinlein, is named "All You Zombies"... but is nothing about zombies..
The movie is only 'good', although I know I'm influenced by the fact that I read the book before.. The main idea is too simply yet so confusing and also excellent.. Please, to anyone that watched the film or read the book, do not spoil the end.. The idea is so amazing that I'd say the movie it's also a MUST WATCH..