>>267647889
It's mostly fun because you're collecting cute combat androids which can be rare. Happiness of scoring some 5* you wanted, but couldn't roll for weeks, stuff like that. Gameplay isn't really all that fun, although building good echelons is definitely amusing.

I definitely had fun for couple months. Also, story is somewhat interesting, especially for a shitty mobile game, i've been often rushing through levels just to see what happens next.