If you want to have an easier time shooting and killing fast-moving enemies such as Geth Hoppers, Geth Drones, and the like, try the following. Open up the command wheel when engaging them in combat. This will freeze the game, but you'll still be able to aim your gun at foes all the while. Aim at the fast-moving enemy and then get out of the command wheel. This will score you direct hit after (admittedly cheap) direct hit.