Something that would be really cool and realistic would be to have dynamic reloading: The way this works is.. the less ammo in the clip you have the faster you reload. Let's say you're using an Assault Rifle with with an ammunition clip of 35. You reload after firing one shot and you reload at normal speed, but if you fire 34 shots and reload you reload very, very fast. This mechanic exists in a game I've played a long time ago but I can't remember the name... So well, it's just an idea :D