There are some solo-variants floating around these forums.
But as-is the game is designed for multiplayer.
Each one works best with the set it has replacement superheroes for for use in Crisis Co-op/Solo
Crisis 1 isn't all that related to its base set, the 'theme' of both was pretty lacking (as these are the first sets, that's understandable).
Crisis 2 itself has a strong theme, but it's closest set (Heroes Unite) is lacking in theme, so...eh.
Crisis 3 and Forever Evil were most definitely designed with each other in mind.