Set years after the events of the first game, Darkspore sees countless Spore species transformed into violent, insane monsters that kill everything in sight. They have been infected with a virus called E-DNA that went from planet to planet, causing ... You know what? It's really not worth explaining. The point is, you're no longer building a cute monster and watching it develop; you are building a killing machine and watching it tear apart its enemies.
Darkspore is so miserable that it even retcons the first game to be miserable. It turns out that in Spore, you weren't a benevolent deity nudging life toward enlightenment. You were a part of the Crogenitors, a race of bored super aliens playing god to amuse themselves. They captured and experimented on less advanced species, and only kept the deadliest to be slaves. If you're a fan of the first game, you not only have to deal with every critic in the world telling you how wrong you were, but you also now find out you've been some space dick this whole time.
Shockingly, taking a kid-friendly game about creation and calling all of its players sadistic assholes didn't go over well. The game's servers were shut down in early 2016.