I'm currently reading XDM: X-Treme Dungeon Mastery by Tracy and Curtis Hickman, published in 2009.
The "deconstructed" magic system in their XD20 roleplaying rules caught my eye - magic-user players simply make up a spell they want to cast on the spot. The DM gives them a target number they have to beat on a 1d20 roll to successfully cast the spell, and they roll another d20 for degree of success.
This magic system is refreshingly simple and sounds fun, especially for young players. Has anyone tried it?
Are there balance issues? Potential for abuse?
As a point of comparison, use D&D 5th edition.