One annoying bit about GURPS Magic's spell classes is that one of the classes of potentially resisted spells needs an extra roll. Douglas Cole brought this up yesterday during a summary of a fun gaming session and Mark Langsdorf discussed it further in the comments.
Resisted Regular spells get one roll - your margin of success on the spell roll is the margin of success your target(s) need to resist by.
Melee spells, though, often end up needing a second roll. You roll to cast the spell, and roll again later during a contest to see if it overcomes the resistance of the target. Not an issue for straight-damage spells, but for spells like Wither Limb or Total Paralysis you need to cast the spell, hit the target, get past his defenses, and then overcome resistance with a second roll.
If there is one thing about me, I hate extra rolls. Even one extra roll is wasted table time, so I don't want to deal with them.
So here are two ways to get around this.
One Roll Melee Spells. If you cast a resisted Melee spell, keep track of your margin of success when you cast it. Effective skill 17 and you roll a 14? Made it by 3. Use that in the contest when and if you hit.
Pros: Simple. One less roll.
Cons: Bookkeeping. Players might dump a spell if they know they barely cast it ("made it by 1, I should just try it again") or target high-resistance targets if they got an awesome roll ("I got a three! I'll go after the Evil High Priest!") (That might be a hidden pro, though, as it adds some real depth to target choice.)
Roll On Contact Melee Spells. Don't roll for melee spells until the caster makes contact with the target. By default, all Melee spells are successfully cast, cost their normal point cost, etc. When the caster actually makes contact, roll the spell roll. If it fails, the spell just fizzles. Success means the defender gets to try and resist normally, if appropriate. The regular rules on pages 13-14 apply.
Pros: One less roll. Even simpler than the above, and no bookkeeping.
Cons: Changes the cost of failed melee spells (from 1 energy if it would have cost at all to full net cost, always.) You can change that by saying you don't pay the energy cost until you roll or try to drop the spell to change your plan of action, etc. Makes them even riskier because a low-skill caster isn't even sure the spell worked until after he tries to get it to go off on a target. Which again, might be a hidden pro.
Personally I've been doing the first one ("Remember what you made it by") but option two has some attraction to it.
If you use either, let me know what you think.