I think the drum mag icons would look better using a pie chart/clock style representation of their ammo instead of the current vertical bar style. I posted this suggestion a while back but nothing became of it.
Reloadable rocket launchers currently have a bug where if you open the voice comm menu, it cancels the reload and swaps to your primary (same effect as if you just fired a rocket and clicked the left mouse button afterwards). It's quite frustrating to say the least, since this bug has existed since at least the second beta.
Bolt action rifles belonging to the enemy team also cannot be reloaded if you decide to pick one up and get ammo from a resupply crate - the reloading animation will play indefinitely, but the ammo counter never actually updates. This is most evident in co-op and can be frustrating if you want to use sniper rifles but someone else on your team is already a marksman.
Melee could use significant improvement - it shouldn't feel like I need to go to USMC sniper school just to smack someone in my damn face. A system like halo (minus the lunging) or even Left 4 Dead 2 would work great, in the former case being that an auto aim for melee could be used, or at the very least, an area of effect that is a cone but not too wide, much like a shotgun, and if someone within range of your melee attack is within the cone, damage will be dealt. In the latter game, melee weapons and shoving had swing arcs, with dedicated melee weapons having their own unique arc patterns. Perhaps weapon bashing could work a similar way in that weapon meleeing would create rays that would be dependent on the animation (e.g. muzzle strike versus smacking with the butt of the gun).
It's also nearly impossible to melee someone who is moving, even if you're still touching them all the way.