What I want most out of the next big first-person shooter is a realistic reload system.
In Counterstrike and Call of Duty, whenever you reload, the remaining bullets in your current clip get automatically recycled back into your total ammo count, so that your magazines always come in full and ready. In Battlefield, whenever you reload, the remaining bullets in your current clip are automatically discarded.
But what should REALLY happen is a mix of the two. Whenever you reload with bullets remaining in your magazine, that magazine should be kept for later use, when you run out of full magazines. Then when you load that particular used magazine, it should have the number of bullets you left it with. Realistic, yes? And to make it even more realistic, occassionaly when you reload, you might accidentally mix up a fresh and a used magazine, so you might expect to pop out with 30 rounds, only to find your gun running dry after three.