I for one don't see why certain basic actions like this need to be tediously controlled by the player. In my opinion, the player should be concerned with overall strategy such as sneaking up behind the enemy, or staying in the shadows so as not to be seen, but not to worry about having to instruct the computer to return fire when fired upon. What sense does it make to be killed when your opponent runs out into the open in front of you, hesitates, and then fires? Why not allow the computer to reflexively attack? To make things more realistic there might be an advantage for the player crouched down and waiting over the player running into view.
Here are some extensions of this idea. There might be a few modes that a player could choose that would direct their soldier to respond in different ways to events. For example, rather than returning fire when fired upon, they might try to take cover or both. How near is near enough to shoot at an enemy automatically? If they are trying to sneak up on someone, they would want to toggle that option off or else to a very close range. If they are trying to snipe someone off, they might set it to a longer range. Also, how annoying is it to worry about how far to throw a grenade? We all know how to throw a baseball and can throw one with reasonable accuracy. Why is it that the trained soldier we are in control of cannot predict approximately where we wanted that grenade to go?
Some people might prefer the current style of gameplay, where the player is responsible for every tedious detail of the game. I for one would rather concern myself with overall strategy, the choice of weapon, the choice of running or walking, from what direction to approach the enemy, and when and how to engage. The current "clickfest" as I call it, where the real competition is in how quickly players can zero in on their target and how many times they can click the trigger button in five seconds, is not enjoyable to me. If it were just me, then that would be my own problem. However, if there is one person that would prefer a different way then there are probably many others that would prefer a different way, and so there would likely be a market for a new product.
Afterthoughts : In games like Counterstrike there is also a problem with cheating by using "aimbots" to automatically aim perfectly an enemy's head and fire. By putting aiming in the hands of the computer and making it the player's responsibility only to choose which enemy to target, this problem would be eliminated also.