Grappling hookfast /ropes - To fire from the groud/throw a hock. To go on top of buildings into windows and down from them. Similar to Battlefield 2 Special forces or a more complex system.
CQB tactics commands & tools - Command you're squad like in Swat 3 or 4 - breach that door with flashbang/clear room etc. Also explosives to breach doors, etc.
SHOVEL dig in and cover the ability to use a shovel to dig a small foxhole or to bury an IED.
the ability to use every door in buildings
Better command system - Christ I hated the commands menu on ARMA II. It isn't intuitive, it's slow & complex and simply annoying. PLEASE make a better command show.
better destruction models - much more detailed destruction when it comes to buildings. Like doors, windows, a floor collapsing, and not an animation of smoke. But detalied on the spot destruction. Also, bullets actually penetrate WOOD and for concret it should be harder.
better animations - like the ability to fire from cover, etc.
the ability TO FIRE you're weapon when on an helicoppter or any other open vehicle
Complex stealth system - amuch more rigores stealth system. Like fallout 3, just more realistic. Add a few stages, so they don't just see you and fire on you. first they think they saw something, and check out for it. Or maybe they are more sure and shoot in the air and/or call a friend to check out the area with them (that way you can destract them or move them around - with let's say planting an explosive device somewhere to distruct them).
customize weapons & self - like a flashlight and a laser on one weapon, personal gear & armor,
Easy and yet full EDITOR - like choosing on what floor I put a soldier, or what load out he will start with, WITHOUT ANY CODES.