As a rule, critics hate everything. And the few exceptions that prove that rule, show conclusively that art's general audience and the art critics are rarely on the same page. This movie is a good case in point. The critics categorically hated it. And lots of viewers who either never knew or forgot the point of what the general public calls sci-fi hated it, too. Unfortunate.
It's of note, that within the writing community (and I means books, not screenplays) sci-fi is usually regarded as an insult. For them, it evokes trite stories of little thought, frequently involving large lizards stomping on cardboard towns in Japan. Among serious writers, the term sci-fi has been replaced with s.f., and it's not just a rebranding. s.f., almost always lower case, stands for speculative fiction. The use of the term is intended to remind writers that if a story isn't genuinely speculative, it's probably just sci-fi (meaning crap, usually). s.f. is fundamentally about speculation, not about sets, actors, directors, budgets, or any of the other things that "critics" like to harp on, perhaps just to sound smart. To be sure, those things do matter, just like the production quality of any art does. Just not as much as the speculation.
This movie contains two core aspects of speculation, one well-known and frequently used, and the other fairly original. The first, of course, is time travel. And it's used in this story in the usual way, to travel back and change the past. Arguments abound in s.f. and in science about that possibility, as well as the practicality. The second is the use of nested time travel. Though it's appeared in a few stories over the years, it's not common. It's very difficult to plan and plot. Planning is the process of designing what happens and why. Plotting is how you tell the audience what happened and through which character's eyes. One of the interesting things here, though not explained, is the amnesia in the subjects. Without that apparently trivial thing, there would have been no story because she would have known everything in the moment she woke.
Think through the plan with me. Wells dies, she finds him. A month later she goes back, as Alex said, and this time, decodes his clue and watch's the video. What's unclear is that if she decides to kill Thomas, why did she need to travel back in time? She could have just killed him in the present. Instead, she protects the video, puts the camera back, buys a rifle and leaves it under her bed. Then she waits several days and sneaks in (somehow) and jumps back a few days, never intending to come back. So did she ever intend to kill Thomas, or just to make her other self think she had? Then she hides out giving her other self warnings and clues. What "other self" you ask? You'll see shortly. She waits for her other self to go to Thomas and get taken into the lab. In the confusion she sneaks in again with her bomb to blow up the time machine while her other self watches her from Thomas's office. She jumps back, the machine blows up, and she becomes her other self with amnesia in the June 2 wake up scene. A straightforward plan.
But the story is only of her other self. And it all works, not because of time travel as much as the amnesia. No, wait. The amnesia, as far as we know, happens after you come back. And she never did come back. Or, did she do another jump, in between, just to come back and cause the amnesia. Or, perhaps she...
See? Isn't that fun? And speculative, even a bit of science (sort of) thrown in. The real measure of s.f. is how long you keep speculating after you finish the story. And, contrary to the critics, this movie delivers. Are there paradoxes? You bet. Are there mistakes? Yes. And finding those inconsistencies is the other half of the fun.
Review by wlfithen from the Internet Movie Database.