Those guns... would rip right off those armatures. Weapons, especially heavy weapons, cause a lot of recoil. I mean a lot of recoil. For comparison, I am going to consider the machine gun farthest back to be comparable to the US military's 240-G.
Do you see the way he is directly behind the weapon with it seated directly in his shoulder? That's important. The recoil of the weapon is actually supposed to travel through his body so that it doesn't affect the aiming point and the muzzle. If those move, essentially you are aiming at a completely new point and the only round that mattered was the first. It defeats the purpose of having an automatic weapon. Besides the fact that this weapon, as it seems to be in the movie, could not possibly overcome this engineering defect, it would probably rip itself right off.
Also, Tom Cruise would be deaf.
There's No Armour
Lets look at that image again. In what is probably the most reminiscently "Saving Private Ryan" battle scene I have ever seen in a sci-fi, there is a complete absence of decent armour. That isn't true. There was this one guy who went in wearing the "heavy" version that had plating. Of course, he also went into battle completely naked otherwise, so whatever. The point is, that battlefield is horrible and stuff that happens in battles like it involve a lot of sharp, tiny, flying objects. This is called shrapnel and it sucks. Nowadays, we wear a lot of armour made to stop stuff like this across our entire bodies and thicker armour for bullets.
In the movie it appears that Cruise wears a police issue flak jacket, intended to stop small projectiles like 9mm to his chest (vital organs). Well that's ok, but it really isn't a good excuse for battlefield armour.
If you're interested the US military actually does want to make this into a real thing complete with actual armour... PS, that would make it an Iron Man suit.
That Thing Is So Slow
I really don't know how to show this because the trailers just don't show how underwhelming these things are to watch move. When you watch their top speed, you realise that you could outrun them pretty easily. They are pretty good at stamina, but in a battlefield, without being able to move, as in move really damn fast, at just some points... you are going to die and that means a lot to all of us who aren't trapped in a Groundhogs day from Hell.
The System Lacks Fine Motor Control
After I realised that those hands don't actually help anything, I really started to wonder how a lot of things got done. They are basically like trying to do everything you need to do on a day to day basis wearing boxing gloves. It really doesn't make sense. And Emily Blunt holding a sword... yeah, that also wouldn't work since they aren't made to improve your grip. There is also a scene where they hotwire a car, without giving spoilers, that should be a lot harder.
Also, I seemed to notice that there is no aiming mechanism at all. Just look and shoot. It's basically all just shoot from the hip... with no aiming mechanism at all. Don't know how that works. Maybe it is why they lost every single day, after day, after day, after...
I'm just saying, aiming is kind of a big deal when you don't have an unlimited amount of ammo. Which reminds me:
You're Doing it Wrong!
So did you know that this whole technology already exists? Yeah, the exo skeleton that Cruise and Emily Blunt are wearing is based off of an actual thing that Raytheon is building. It's nowhere near ready, but still... something looks familiar.
But it isn't made to make a regular "untrained" soldier into a super soldier, at least not the type of car crushing one. It's made to just make them really strong as in "load bearing". This is one of the most important images for how this technology will be used.
As a former Lance Corporal in the Marines, I know the truth. They just want this technology so that we can carry more stuff. Honestly, that's what its going to be for. Expect to see future Marines wearing armour like this packed floor to ceiling with massive "turtlebacks" overflowing with extra ammo, weapons, food and supplies, medical equipment, and probably adult materials. I'm just being honest.
What wasn't featured at all? Anyone on that battlefield with extra anything. It just simply made no sense. In fact, there is a moment in one scene where Cruise says with manly bravado, "give me more ammo and another battery" (see Advait's answer about power). I am sure to non-military this delivered the intended message that, "Oh, he's growing as a warrior. He's much more prepared now." What the rest of us who have ever been in were thinking was much more like, "What the Hell?! You mean you haven't had full ammunition this entire time? You're a friggin idiot!"
The truth is that in the battlefield of tomorrow there will be a few guys in every squad who are simply caring massive, massive amounts of extra gear like what I am describing.
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What are the cons of a real world military jacket, as portrayed in Edge of Tomorrow? originally appeared on Quora. You can follow Quora on Twitter, Facebook, and Google+.
This answer has been lightly edited for grammar and clarity.