put some strategy into base defence
So I was thinking, I really don't like turrets at the moment. They are way too powerful, and are often used to replace marines in locations actual marines don't feel like hanging around in. Part of the problem is that turrets are necessary, so they can't be overly expensive, but because they perform a pretty simple task (shoot things with bullets) comms usually just overkill with them.
So I was thinking, make turrets customisable in terms of what they do, but add an expense to the upgrade. This way turrets fulfil a specific role, and the cost may put comms off spamming many of them. The customisation I had in mind was; Machine gun turret, grenade turret, and flame-thrower turret.
So, when you first place a sentry turret, it is just that, a sentry. It doesn't shoot, it just alerts the commander to the presence of an enemy, and maybe it places the motion tracking sprite over the target as long as it can see it. It costs exactly the same as it currently does. If the comm want's it to do damage, he can spend some resources (maybe 5 or 10) to upgrade it to a machine turret. It loses the sentry abilities, but now takes the form of what we currently know as the sentry turret. Once the commander has researched grenade launchers, he gains the ability to upgrade a turret to a grenade turret (10-15 res). If flame-throwers are researched, a flame turret can be created(15-20 res).
A commander can use these to strategically defend his base rather than the current spam we see. Put one flame turret at each entrance to toast anything that comes in, some grenade turrets further back facing the entrances to cover a retreat, and machine gun turrets in the usual place.