Counterspell could also be an action or free action to give a generic spell failure % for a minute. Like a hex visualized by some arcane runes surrounding the target. Or it could trigger a d20 contest on cast attempt. And it would be dispellable.
The d20 attempt would be a rather good solution too, but I doubt Larian will go that far. The other major thing about Counterspell is that while it automatically counters everything on the same spell level it was cast at or below, spells cast at a level higher than the counterspell means the counterspell caster has to roll higher than the spell's DC using their spellcasting modifier to counter it.
If counterspell is implemented in this way, the latter part is probably going to be massively amended somehow. I don't see Larian spending much time to code in different DCs for spells relative to the spell level that counterspell is cast at.
