Looks good, no scratch that...looks great for your first dio...but here are a couple things to help you get better.
1) Snow, unless it is newly fallen is not pure white, mix in some earth tone pigments into your snow to give it a "muddy" appearance.
2) Sandbags are really easy to make out of 2 part epoxy, I use Aves, and it is great! Not that expensive and it gives you a LONG time to make them. Your sandbags, and I understand they are "premade", are huge! A good general rule is to get a standing figure, and make the sandbags the same size as the distance between his foot and knee, maybe a little smaller. You can use medical gauze presses gently onto the bags to give them texture, and a small toothpick or dental pick to put the seam around the middle. Like I said Aves is great stuff and it gives you at least an hour to play around with it.
3) Finish the "story" the tree stumps look great, but where are the trees? Where are the fragments, or the saw dust, or the branches? Empty shell casings, other "lived" in evidence.
4) The figures are REALLY well done, just need some evidence of wear, and others have given you some great advice.
Great work, very, very well done!