Playing Pool Of Radiance got me learning the ins and outs of 2nd edition AD&D and I came to the realization today that I prefer games with a magic points or mana system. Probably because I grew up with JRPGs which exclusively deal with MP over spell slots. Don't get me wrong, D&D is great, but it's such a pain when you get into battle and you realize you forgot to memorize Detect Magic and now you have a bunch of potential good loot.
I would argue that FP more or less function as mana points in the default/GURPS Magic system.
Also, what splat are you referring to in the second paragraph, Thaumatology? RPM?
Thaumatology. And nothing says you have to spend FP to cast spells. It is suggested as a possible default way of doing things, and GMs will often make you do that, but it's not a hard rule.