This is so cool, I really like the guy who is standing there as though he were in shock. He adds a lot of contrast and characterization between him and the guys that are hugging cover. Great details too.
"The men donning full-faced helmets are Coalition Marines, professional soldiers.... Hmm, do the aliens use chemical warfare, then?
On a side note, the CMs' helmets appear strongly of German design....
"...the other two are colonial guard, the colony's militia, so that should also explain why the two kneeling seem more shocked and anxious than the others."
Ah, I hadn't picked up on that. I'd assumed they were infantry walking point (the other two, now ID'd as CM, I'd taken to be drivers), and the explosion had forced them to take cover against shrapnel behind their assigned vehicle. From their expressions, I'd thought that they'd either been very surprised (and this picture was "taken" an instant after the detonation), or that they'd had buddies in the destroyed APC.