Just finished an ME 2 run with my Engineer. It was basically a no-guns run, where I used my weapons as little as possible (meaning I only used my SMG early on while my powers cooled down and the Cain at the end). Inmstead, I maxed out my Combat Drone, Flamethrower, and Dominate for lots of fun and Collector-kicking.
Too bad Dominate's not in ME 3. I'll probably go with Defense Matrix because of its cooldown bonus.