This article won't be our typical movie review. Why Edge of Tomorrow is an entertaining movie you can read in a lot of reviews all over the Internet so let's concentrate on the question why the film is a mess. This will hardly happen without any spoilers though so be prepared to encounter them.
Edge of Tomorrow is a science fiction film about an alien race trying to conquer the Earth. The aliens are called Mimics, which actually does not matter for our purposes. The alien race (or organism) consists of three different species: first, countless "disposable" ordinary soldiers, which are easily allowed to die; second, much more rare and valuable "Alpha" Mimics used as scouts to improve the alien race's cumulative knowledge; and third, a unique Omega Mimic, which is the brain of the hive and stores the accumulated knowledge. Whenever an Alpha is killed, the Mimics possess the ability to reset time and use the gathered knowledge to improve their performance in the next time iteration. During his first actual battle, TV star Major William Cage (Tom Cruise) is killed by an Alpha Mimic but since he is covered in Alpha's blood in the very moment of his death, he inherits the ability to reset time and accumulate knowledge. Subsequently he tries to use this ability to destroy the Omega and in the process, he is helped by Sergeant Rita Vrataski (Emily Blunt) who used to have the same time resetting power in the past.
As mentioned above the movie and the story are actually entertaining but also the same interesting time-loop concept is where the problems with the movie begin. There is not a single good-enough explanation how the whole time resetting thing works. If we take, for example, the "Cage" case introducing this concept to the movie, it's not clear who resets time - whether it's Cage or the aliens being it either the killed Alpha or the Omega. If the aliens are the reason for those resets, they should accumulate knowledge as well as Cage and improve themselves. If Cage is the one triggering the resets then it still makes sense to assume the Omega preserves knowledge as well otherwise it would be quite strange to think the Omega would know anything about Cage at all in order to send visions to him. So, we can safely assume that the alien race retains its ability to accumulate knowledge and improves in parallel with Cage during the time resets related to Cage. And now the questions begin.
First, is it plausible enough to think Cage will improve "better" than the aliens in order to accept the filmmakers' idea he will be able to defeat the aliens this way? Isn't it more likely that the aliens will be superior in this process since they've been doing it for a long time? It does not make sense to expect from a beginner to beat the professionals in their game. If we somehow accept it, the next question pops up. After Cage dies and wakes the previous morning, why wouldn't the aliens just kill another Alpha and reset the time to an even earlier point thus preventing Cage from access to their essential time-resetting power? Both of these questions leaved unanswered should probably lead us to the conclusion that the alien race is actually quite stupid.
But here comes the last question in this vein. If we somehow accept the above "stupidity", wouldn't the aliens be at least so smart to have always an Alpha ready to be sacrificed at the slightest possible danger for the Omega. Why would they risk the life of the Omega at all if they have the ability to reset time by killing an Alpha? Cage says to his crew just before the attack against the Omega near the end of the movie that it is very important to avoid killing an Alpha exactly for the same reason. And simultaneously we are forced to believed the aliens would not do such a killing themselves in order to save their hive mind. I'm sorry but independently of how much I'm trying to suspend my disbelief I would not buy that last one.
There are also other discrepancies in the movie like, for example, how it happens that nobody recognizes the famous face of Major William Cage from the TV. Since these issues are not related to the time manipulating concept we can omit them for the purpose of this article. And to bring it to an end, Edge of Tomorrow is enjoyable and the movie has its merits but if you try to think about the concept the film and its plot are based on, you'll end up in a great confusion.