That's a bit of an optimistic stance to think that the AI will automatically get better with a cover system. They'll duck into cover and shoot blind, then pop up to die, heh, like in most other games. But anyway, I use cover already, I'll back up to a wall or a piece of wreckage and hide behind it, it didn't make the combat feel tactical though (takes far more than a cover to make the combat tactical).
That's not how AI works in a good cover-based system - it gives the AI something else to do other than blindly run around, for one. Also, running in front of a wall doesn't offer quite the same advantages as when there's a mechanic worked into the game for it. You can't set your shots up before popping back out to shoot, for one. Or use that view to get an idea of where your opponents are. Adding in some tactics for them to use besides "run around like crazy" isn't going to make them any more prone to stupid maneuvers like shooting at random, any more than it's currently set up.
Putting in tricky AI and all the trappings that you get in a modern FPS though, is going to make that frustrating at times for the non-twitchy RPGer.
You're saying that adding in the standard trappings of current-gen shooters is going to make the game too twitchy, and giving the enemies more intuitive tactics would frustrate non-twitch players. Yet I get the feeling you would also like improved enemy AI so that they're not shooting at walls. Frankly, these games are easier for me to figure out when the enemies do roughly what I would expect them to do. This randomly running around stuff (or just rushing straight at you) that I get for the most part in Fallout 3 is more frustrating than if the enemies used cover in a moderately realistic manner.
I honestly can't imagine anyone saying "Why do the enemies have to carefully and systematically try to manuever into strategic locations instead of just running wildly and trying to get behind me?
If I had to make a change to combat though, I'd prefer tougher opponents just in terms of their HP, so to speak.
That can get you into some real problems, too, though. Eventually it stops making the combat harder and just makes it more annoying. Like Mass Effect at the hardest difficulties - you could blast enemies with your tank's cannons, blasting them over the horizon, and it would barely make a dent in them. It became a matter of trying to keep the enemies in your sights long enough to do any actual damage than providing any sort of added strategies - in fact it usually took away from it and encouraged standing in one place out in the open trying to keep your fire focused on one character at a time.
I'd rather go with lower HP for the player character, if anything - or greater damage from NPCs. That'd make it harder while also encouraging more intelligent use of the game's mechanics to stay alive.
Also, for me it's easier having a button worry about getting me into cover - otherwise I have to spend time figuring out how to position myself the right way, and I can't check out my situation without bringing myself out of cover (there's not even a "peak" button like in the Half-Life type games.) As a less twitchy player myself, I'd rather have a "panic button" I can press to get myself out of trouble - it's one extra button, at most, to implement - these days I don't think that's going to be much of a hindrance.
Anyway, I'll move onfrom this because you and I aren't going to have anything to say that's not just repeating ourselves once again.
A more accurate way to do it would be to calculate the percentage of your body that's visible and use that amount, but that sounds too complicated. Regardless, there should be those thredd shooting stances. If it takes a second of gametime (and AP in vats) to move from one stance to the next, then the tactical challenge becomes to balance the benefits of the stance with the liabilities. That is, being prone may improve accuracy and cover, but leave you very vulnerable to melee attack.
That's fairly close to how it works currently - the chance to hit a body part you're targeting is modified by what percentage of the part is exposed (which is why it's easier to hit the leading leg, or the arm that's facing you in VATs.) So crouching behind cover is going to have an actual effect.
I also think crouching raises your accuracy to some degree. And it'll make you a little harder to hit as well, I think.