There are two types of mobs in this game - ones that can be easily taken care of with the Barrett, and... hmmm. Excuse me, I seem to have miscounted, there is ONE type of mob in this game... :P
I like the game, but the controls are a bit iffy sometimes. Trying to go invisible and jump at the same time tends to do one or the other, but not both.
1948 is easier than it looks... use speed boost to stay ahead of the enemy planes and use the poison cloud as much as you can - as long as you don't fly off the edge of the map or let the enemies get in gun range, the poison cloud will take care of all but the flying wing, which you can then get behind and shoot down without getting a scratch.