Steppenwolf, as he came to be in Justice League, wasn't really the most compelling villain, but he could have been more interesting than the film let on.
In this featurette from Justice League, online via Flashback Filmmaking, the creators of the film (sans, of course, Snyder and Whedon, whose conflicted roles are quietly avoided in the special features) run down what makes Steppenwolf interesting to them, and in the process they get at what could have made Steppenwolf interesting in the film.
He's a fixture of Kirby's wild Fourth World, uncle of Darkseid and yet his servant, caught in a cosmic Shakespearean conflict for power, prestige, and dominance over all life. All of which is really interesting stuff, and that consideration makes this featurette worth watching, if only to imagine what could have been.
Instead, the Steppenwolf on film will go on down as a guy who... really likes Mother Boxes, I guess?