I'll preface this with that I actually solely play the competitive mode myself and the features I am proposing are not really ones that I'd be needing for myself. Rather, I believe that these features are more or less mandatory to get casual players play the game.
So, reward mechanisms. People play games and really, do anything at all, because there's some sort of reward. In games, no doubt the simplest reward would be winning your match. This reward however does not come very often nor does it come every time. Therefore there needs to be other mechanisms of reward in the game. For example, in Battlefields you get points for supplying your teammates, you get points for standing on a capture point, basically you get points just for breathing. This makes the gameplay feel rewarding even if you don't win the whole match. The game still continuously rewards you for things it thinks you did right. Even in more hardcore shooters that have at least some casual appeal, say Squad, you get points for e.g. being near your squad leader or for supplying covering fire and so on.
In Insurgency: Sandstorm, you don't really get this feedback. You only see your score when you're dead and the only things that give you any score are your kills and point capture (and well, assists, but those are rare). I think the game would benefit from more immediate reward and other feedback mechanisms. This doesn't mean that it should be all CoD, or that e.g. kills should be announced to the player. But more immediate rewards would either way make the game more appealing to the casual player.
Therefore, I suggest that in the Versus mode, player would get score feedback right on their screens from actions such as defending and capturing points, giving suppressing fire in cases where the enemy would have made a sound anyway (so that the points don't give away the enemy's presence), and so on, to make the gameplay feel more rewarding even when you don't win the match.