I liked the time loop premise. Sometimes it works, sometimes it doesn't, and for me it worked in this movie. Watching him die over and over again was funny at some points, drawn out in others, but it kept the plot moving. It really was a video-game mechanic. Die, respawn, alter strategy, die, respawn, remember spawn points for the enemy.

I didn't like the 'happy' ending. I would have preferred everyone who died stayed dead, because it is war after all, but have a similar scene to the one we get at the end. Mysterious pulse of energy removing the ability for the creatures to fight, and humans reclaiming the world from the alien invasion. Maybe they eventually find the bodies of J Squad and put together the pieces, and they're posthumously honored as international heroes. But I haven't read the book, so I don't have room to judge until/if I do read it, and people everywhere are arguing and debating over what the movie's ending actually means.

One idea that I've read and liked was you have two different 'save' points. One for the aliens, before Cage got the alpha blood, and one for Cage (the day we keep reliving). You have to keep in mind that the Omega exists in multiple points of time, not just the present and past. That's part of how it can control time (to an extent). As it was dying, and as Cage was dying, the omega blood got into Cage (giving him the ability to loop again), and it tried to "respawn" to the most recent save point (opening sequence). However, because it actually died in the 'future,' it actually died in all points of time that the individual Omega was present. Because Cage had the Omega blood, he respawned to that same save point, but WITH his memories still.

It's the only theory I've read that actually seems to make sense. In a Doctor Who kind of way.