Quite fumbly when it comes to longer reads, but quick reference it is best.
Also sucks that it has yarr harr fiddle dee content so, even though its CR calculator and loot generator are some of the best i've ever seen, i can't recommend them to anyone.
Videogame turn combat is actually borrowed from TTRPGs. Old D&D editions (mostly 1e) had a combat system that was pretty close to what you'd find in a modern RPG videogame, just within the constraints of the table.
In GURPS, you expend either Fatigue Points or Hit Points to cast a spell.