I like the magic system in Cinematic Unisystem - you have to roll a skill check to cast a spell. You need so many levels of success or something 'bad' happens. There's fatigue in the form of penalties to future spell rolls - you can get one or two off pretty easily, but more than that and you're going to get tired. Spell slots feel clumbsy but workable, mana points are more 'realistic' but a PITA to keep track of. Fatigue that does hp damage has the unintended side effect of making wizards into bull mooses with huge CON scores. I'll take my wizards frail and scholarly, thank you!