I've found that I'm getting used to the cover system, though your placement has to be pretty spot on in order to use cover, I'd like to see the proximity to an object widened so you can jump behind it for cover quickly instead of milling about around the pillar or what have you for ages getting your butt kicked.
It's been my experience so far that the melee character really can't use cover. You can use it to hide from stationary guys shooting at you, but at some point you have to come out and close the gap to face tank them, basically rendering the cover system of little use.
What about a system where you can crouch behind your shield for cover? Then you could utilise cover when fighting face to face and your shield could have an amount of cover that gets degraded as it's hit, breaking the cover at a certain point and then it needs to recharge.