GMMichael
Guide of Modos
Part of me says that this is a major consideration: is a game still fair if wizards can stop fighters from fighting, but not vice-versa?I think it's bad that there's no way for a fighter to make a wizard stop being able to cast spells (except beating them dead), but there are plenty of ways for a wizard to make a fighter stop being able to fight.
But another part of me says that comparing fighters to wizards is like apples to oranges. Whoever said that magic has to be fair? That gets muddier if the fighter has access to one or more forms of magic - like a ring of (magic) protection.
From an action economy standpoint, it's a different discussion. If the monster's big, special move (or wizard's 3rd level spell) takes three actions to complete, but the PC interrupts the first action with her own action, then both characters are only out by one action, right? The tactical decision by the PC was, "do I want to attack, save an action for attacking, or burn an action to attempt to disrupt this special move before it occurs?" For the GM (or game designer) it's, "is the game less cool or fair if combo actions aren't guaranteed to occur?"
@GrimCo , doesn't Pathfinder do it the other way around? The spell takes only one action (unlike the above three) but is interruptible, while the fighter gets multiple attacks/actions in a round? I suppose there were some full-round-spells, which would be really annoying to attempt to cast.
Now I'm leaning toward yes, interruptible, BUT depending on what the power is, and the nature of the opponent. Maybe a squishy wizard wants a sturdy Wall of Force in the way, while Godrick the Grafted doesn't give a flying dookie if you slice off his leg while he's charging you. I think that opens up some territory for wizard perks like Instant Spellcasting, or it gives the GM room to make situational calls (per @Theory of Games ). The former is the D&D route, with lots of neatly interlocking rules, while the latter doesn't work so well for PCs and GMs who like things in black and white...