In video games, I think it was Magicka wherein you could craft your own spells more-or-less on the fly.
In TTRPG, Mage: the Ascension, for much the same reason.
The issue for me is that I want to feel like I know Magic. I want to feel like a wizard, shaping the power of the cosmos to my will. If all I have is a collection of pre-scripted tricks... it really doesn't matter how many pre-scripted tricks I have, the feeling of creativity in spellcasting is lost.
Magicka is amazing for short burts of coop fun.
However, at some point you find that one spell that is just too busted and trivializes everything, until the DLCs decide to chuck a billion enemies at you.
From a technical standpoint, it's also a bit rough around the edges and likes to crash to desktop.
Definitely a decent investment if you can pick it up on sale.
Magicka is very interesting, definitely one of the more unique spell-casting systems (and it feels like a real system). Unfortunately I'm not good at it, it's pretty fast-paced and I die so much. xD