When looking through the store for games that might interest me, I tend to want specific types of games.

For instance when I look for a "Roguelike", it would be nice if I could filter out "Roguelite" or perhaps "Action" as I prefer roguelikes to be turn-based.

Of course adding turn-based would help, but that also might exclude other games I have not heard about and might want to try, but would otherwise be filtered out by doing so.

Therefore I suggest:
For every tag you can add also make it possible to subtract it.