There's been a lot of discussion about the chaingun already so if the developers are sick of hearing about it by now I apologize, but I know I'm not alone in thinking it still needs some tweaking.
My issue is that the chaingun is a mindless weapon. Unless an alien takes you by surprise or you are already hurt, you can pretty much count on killing anything that tries to close the distance to you just by holding down +attack and training your sights on it. I see three downsides meant to balance the chaingun:
1) Its inaccuracy. This is good, it gives soldiers a fighting chance and entices humans to crouch to increase accuracy, exposing their heads and slowing them down.
2) Its ammo capacity. I do not see this as much of a limitation. Any cautious or otherwise smart player (one that doesn't want to feed) will only make short trips away from the base with the chaingun to rack up credits and then only attack the alien base with the cover of teammates. In either case the risk versus reward is quite low. I'd say the ammo limit is more an encouragement to boring, defensive play style.
3) Its cost. This is essentially irrelevant once you get the chaingun and are able to consistently get more credits by not putting yourself at too much risk. Four hundred isn't really that much, but being even a slight hindrance only makes people play even more defensively with it.
I've used the defensive chaingun technique with great success, easily taking down dragoons and lesser classes bored into attacking. To fix this I propose making the chaingun overheat if a player sustains fire for too long and the hotter it gets the longer it takes to completely cool down. This would not only give aliens a chance to reach melee range (by either forcing a player to fire in bursts or penalizing them with overheating) but would reward humans that fire intelligently instead of just spraying lead until something dies. It would make the chaingun a more interesting weapon, differentiating it further from similar weapons, like the lasgun (the only major difference between the two right now is accuracy). Most importantly, it would require some amount of skill to wield effectively, making things more fun for both teams. To offset this I say increase the ammo capacity to around 300. With both these changes I think humans would be more aggressive and aliens less stressful to play. What does everyone else think?