Riffing off my ideas from this thread on the SJG Forums, here is an easier version of Counterspell. This makes it a much more useful spell, faster in combat, and allows for more anti-magic magic use.
As per GURPS Magic, p. 121, except you may attempt to counter any spell, even if you don't know it. If you don't know the spell you are countering but it's a commonly known spell or you've used Identify Spell on it, your skill in the Quick Contest is at a -5 penalty. Unknown or new spells, or spell-like powers with the Magical limitation, are countered at -10.
Time to Cast: Same as the spell being countered, not counting time reductions due to skill by the caster of the original spell; maximum 5 seconds.
- Breadth. You can now try to counter anything, known or unknown.
- Prereqs. You don't even need Magery 1 for this; Magery 0 (or nothing in a High Mana Zone) is enough to learn this and cast this. A small change, but there you go.
- Time. Basically if you're countering a 2-second spell by a Skill-20 caster (so he did it in 1 second), it takes you 2 seconds to counter (1, if you've got Counterspell-20). If you're countering a 1-hour to cast spell, it takes you 5 seconds to counter it (3, if you've got Counterspell-20).
You may try to Ward a spell you don't know, or know at a level below 12. However, you are at -5 in the contest. If the spell is completely unknown, or it's a spell-like power (one with Magical as a limitation), you may attempt to Ward it at -10.
Another option is the Technique. That is, there is no Counterspell spell. Instead, all spells come with a Counterspell element. In this case, you counter a spell by casting the same spell. You can remove a Create Fire area with Create Fire. Cost is 1/2 of the cost of the spell countered; time to cast is the same as the original spell. Any usage triggers a Quick Contest of Skills. Roll against your own skill at -5. You cannot Countspell against spells you do not know.
Then you'd want a Perk, perhaps like this:
For each level of this perk, you roll at a +1 in the Quick Contest of skills. Maximum 5 levels. This works for all spells you know - you're just good at undoing magic.
If my players like this, I may try the first option (you can counter anything) - it's a broad power give to wizards, but it means enemy wizards can take Counterspell and Ward and have it actually matter. Dispel Magic is still a better option for brute-force removal of multiple spells, and it can be left alone IMO. It's kind of funny that the "surgical" option (one spell at a time) is easy and the brute force option (all spells) is hard, but Dispel Magic is cheaper and big, and suffers nothing from your lack of knowledge. Counterspell works best under this option if you stick to what you know, but Dispel Magic works no matter what.
I'd limit Dispel Magic to 6 seconds maximum Time to Cast, too, but that's just me.