I like how recent patches have improved marine combat to make it feel more fluid and modern, but there is one element that I still find very bothersome. The backward walk is ridiculously slow, so much so that it feels cumbersome. I understand that this is a balance issue, it helps the Aliens close distance with the Marines... but the tradeoff is too great. I cannot think of another modern first person shooter where moving backwards is so heavily punished.
I think Natural Selection 2 should model the basic infantry level combat after a game like Left 4 Dead. Both games involve asymmetric warfare. One team carries guns and the other can scale walls, leap great distances, etc. On top of this, the mechanics of combat are similar for the Marine and Survivor teams. There are no iron sights, prone, etc. The only difference I can think of is that Marines can sprint. Anyway, the point I am trying to make is that Left 4 Dead is very popular, partly because the shooting mechanics are very fun. If Natural Selection 2 can achieve that same level of satisfaction in wielding a weapon and gunning down Aliens, then the game will be more appealing to new customers. Restricting player movement in anyway hinders this, so I would like to see the very punishing backward walk speed increased significantly.