Defense Grid: Containment came about from a Kickstarter campaign intended to raise enough money to create Defense Grid 2. Sadly, Hidden Path Entertainment didn't get the funding needed to create a full sequel to this amazing tower defense game, but the studio did manage to bring in enough to make some new DLC.
Containment has the same amount of content as You Monster, but feels bigger to me. The maps are more interesting, the challenges are harder, and it just feels like a bigger addition to Defense Grid. It's money well spent in my opinion, and I can see myself playing through these maps until I achieve perfection, no matter how painful that may be.