I grew up playing Goldeneye 007 on the N64. Thought the cheat menu you could go through the entire game using whatever weapons you wanted. That was the most fun.
Most FPS games these days don't that "that gun" you know the favorite stand-out weapon that everyone goes, "I love that gun I took it through the whole Campaign." Halo:CE maybe have been the lst game to do that with it's M6D Pistol but I've gone and let my imagination run away.
If they can give me unlimited ammo it could make the game interesting. Seeing through walls and killing scripted bad guys before they have a chance to suprise you is always a blast.