Just to add some more variety to the weapons, I think it'd be great if shotguns were reloaded by the shell and not in magazines like all the other ammo weapons. You press the reload button to start refilling shells, one at a time, this can be stopped before it fills up all 8 shells by pressing fire. That way you have the option of reloading just a shell or two to quickly finish off an alien.
Of course, this would result in some other tweaks in the shotgun, to balance it out like it is now. Reloading all 8 shells would obviously take longer than it currently does (I'm thinking about 4 seconds, 500ms per shell), however it also creates the option of reloading in a SHORTER amount of time than it currently takes by only reloading 1 or 2 shells. And the longer reload time would decrease the damage per second of the shottie, so the cooldown time between shots would have to be lowered or the damage increased.
Anyway, it's not like it's anything major, and it could easily be more trouble than it's worth. But a regular shotgun reload would be a nice addition to the human reload system, imo.