For those complaining about the bloom lighting, keep in mind this isn't Earth, the game is taking place in a post-apocalyptic setting, after the humans used a scorched earth policy. I'd imagine the ozone (assuming Sera ever had one) is pretty much toast. I'd expect the kind of lighting we're seeing in these shots given the environment.
As to the armor, as has been mentioned: they're fighting the Locusts, a race that can take a massive amount of damage before going down, and likewise can dish out a lot of damage. You don't want to fight the Locusts in a pair of sweat pants or GRAW-gear. Besides, all that blood washes of that armor pretty easy.
If there's a question to be asked about the armor, it's why is Marcus wearing it while in prison?