Force Jump. Go ahead, laugh!
If I had to choose one power, this would be it. It's so integral to gameplay you forget it's even there and take it for granted.
Without Jump you couldn't navigate the map as quickly as you do, you also couldn't do any of the acrobatic moves you do with ease. It's essential for both escape and pursuit.
Jump allows you to get over obstacles and get an angle on your opponent for sniping, and to fire rockets in his face so he can't push them back. It allows you to dodge his shots until he runs out of ammo.
Needless to say acrobatics are essential for confusing the enemy and getting to powerups and occasionally to cheat death from those falls that normally kill.
You don't appreciate having Force Jump until you take on the role of a Merc in siege. All of a sudden you're Mister Slow Pants with his "normal jump" of 2 feet. ; )