Play the entire Creeper World series:

The main enemy, as always, is "creeper", a thick fluid that floods across the map, fueled by emitters that keep it flowing. Its movements are predictable. It creeps around hills and through valleys happily submerging anything in its path, including your base. Its strategy is limited, but capacity for generation unending. Destroy the emitters, though, and humanity has a chance at retaking the planets it affects. Each level starts with placing a command base of operations, preferably on high ground. Powering your siege will require connecting collecting nodes placed and linked around the map to mine Build Packets out of un-crept upon earth. These nodes send energy to your command module, which then sends it out to various weapons, like the fast-blasting Pulse Cannon or slower-but-impactful Mortar Launcher. Using weapons to hold the creeper at bay will allow you to claim more ground for energy collection, meaning more energy to power new weapons and moving existing ones to new locations. Once you get in range of the creeper emitter, you can build a Nullifier to eliminate it. It'll require a lot of energy, though, so keep your supply lines moving and your weapons powered. Eliminate all enemies on a map and you've completed the mission! Later levels will unlock new structures and weapons, like energy-creating Reactors, Ore Extractors, Sprayers that can convert ore into a similarly-flowing-but-on-your-side Anti-Creeper, and Terraformers that can change the lay of the land to your advantage, and new enemies, like Creeper Spore Launchers, to vex you.

I first encountered the Creeper Series in its Creeper World 2: Academy variation, and while I am sorry to see the unique side-view and its physics go, I have to admit that the return to the top-down view of the original Creeper World gives a more natural war-room-like presentation, if a somewhat more visually imposing one. Though definitely welcoming to new players (if a little light on documentation), be warned that it is a game that will soak up a lot of time, tailor-made for the kind of strategic gamer who prefers sieges to blitzkreigs, or tower defense fans who want a bit more of an active experience. It's hugely satisfying to claim victory after a protracted battle and it's always a nail-biter right up to the end. You'll be left wanting more, of course: more maps, to make your own mission, to see how the Creeper World community is pushing an engine to it's limit. That's part of the point of Creeper World 3: Abraxis was created. But either on its own merits or a teaser to something more, it is a worthy installment, and you don't need to be Homer Simpson to see the merits of free goo. (Mmmmm.)

Play Creeper World 3: Abraxis