CoD series - Remove all idiot friendly perks, balance weapons, remove claymores and other assorted free kill bombs and such completely.
Halo Reach - Disallow armour lock from most standard Slayer games and increase its recharge time
S.T.A.L.K.E.R. - Weapons deteriorate much faster
Crysis 2 - SO. MUCH. LAG. MUSTTTT FIIIIXXXXXX
Dawn of War Dark Crusade - Revamp Space Marines, Chaos Space Marines and Necrons so that they are generally ridiculously powerful but also ridiculously expensive. Should mix the gameplay up a bit...
(If anyone knows a mod that does something like this, I'm all ears, or eyes or whatever)
Original Age of Empires - Remake it with fancy ass graphics and chuck in some new units and campaigns.
Seriously, this was like the most awesome RTS ever. THE VILLAGERS HIT PEOPLE WITH GIANT BONES!
Mass Effect 2 - Completely change the combat. I don't care just what it changes into, just freaking change it.
Metro 2033 - Errrmmm....hmmm....
Deus Ex - Give everyone what they want and give us an alternate campaign where you stay with UNATCO and fight the actual bad guys.
-
Ah, one can dream.