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.
The most glaring downside to magic points is that unless there's further limitations it means "cast the biggest stuff and have nothing left for anything else" which has metagame consequences such as the rest/recharge economy getting even wackier and the fact that encounters would have to be balanced against front loaded maxed out spell attacks.
I've found "drain" based systems work better there, especially ones where lesser spells can be cast almost indefinitely.