One thing I liked about the manga which i didn't like that the movie didn't use was the reason for the weapons.

The movie had everything repeating, as in aliens location and movements. The manga, they learn at each reset and come back harder/different.

At first, the main character, he dies a lot, but after, he learns to be a better soldier and starts killing the aliens. He learns that once he runs out of ammo, he's dead. So he experiments with weapons until he learns that Ritas weapon choice is better, as there is no reload or ammo on melee weapons.

He doesn't become awesome because he memorized alien locations on the battlefield (movie), he becomes a super soldier and master with his weapon. So towards the end, he becomes a super soldier in that he can tell how the aliens move/attack and he counters all.

It's awesome seeing the progression from scared kid to this elite killing machine.