I've spent insane hours grinding different Gears games, but returning to Lost Planet 2 every few years makes it my longest achievement grind.
free 1hr completion, why not?
Bird of Prey - Kill 25 footsoldiers using your rocket pack guns - Dark Void
99 Red Balloons - Kill 10 enemies while they are in an anti-gravity bubble - Dark Void
I'm a Rocketman, Baby - Perform 100 special maneuvers with the rocket pack - Dark Void