I feel like a lot of people sleep on Orbital Gas Strike, but I really love that thing. For starters, it's great for smothering a bug breach, drop it on the breach when you first see the ground crack and it'll kill all the small stuff. Same with bots, drop one where a bot drop is about to land if you don't have a way to take down the dropship and it'll smoke anything smaller than a devastator, including the pilots on the scout walkers.
The gas lingers long enough that if you're being chased by a swarm of something, drop one just behind you as you run away and they'll march into it, and only the strongest will come out again, leaving you free to focus on the big things.
Plus, it'll blow a bug hole on a close hit, a bot factory on a direct hit, and has a very short cooldown and easy sequence.
Orbital Gas Strike, smells like Victory.