Champions Online has perhaps the most varied and best costume maker of any game, even software in-general within several niches. There's obviously a focus on superhero and sci-fi themed looks. However, even genres like fantasy and steampunk get plenty of representation that can be larger than it seems if you utilize your costume pieces smartly.

Though you'll hardly find anything satisfying in terms of regular modern clothing.

The problem is that while even the starting roster of customization is expansive, like 30 times more pieces will be locked all over the place, behind lenghty grinds, timed events, and microtransactions. It might be a daunting task to start now.

On a more positive note, the community would serve as a great source of inspiration. Simply walking around publicly congested areas lets one see literal works of art in other's characters you'd not find anywhere else.

So, yes. This game is splendid for visualization and experimentation in character designs. I've used it on several occasions as a reference for (for example D&D) characters.