This suppliment made all the difference!
While the CORE rules are great in many ways, they were a little lacking in flavour for spells. The difference between shooting a bow and casting a magic beam were mechanically the same (except different 'effort' dice, and 'tags'.), which left a lot of flavor up to the GM to describe. But ICRPG Magic fixed all that.
I was skeptical when I first browsed the pdf. I was worried the extra bulk of magic rules would take away from the simplicity that made ICRPG so great. But the rules were a breeze to play and added so much added flavour (and effects) to the game. Simple spell blasting and endless heals have now been replaced with crazy vampiric mists that suck life from enemies and heal your allies, or unnatural winds that blow your advisaries back down the corridor away from your group.
Yet the rules are still lose enough for immproptu and narritive style that encoumpasses ICRPG.
I was also worried that characters must sacrifice (cost) Hit Points to cast spells. But some of the old-school players loved this, pointing out that in early editions of D&D, wizards had very few HPs....with ICRPG all characters start off with 10 HPs (a heart) but now with Magic costing HPs to use, it once again makes spell-casters generally low on HPs for most of the encounter. This was a brilliant design.
On top of all that, ICRPG Magic also has additonal monsters and adventures, making this a 'must purchase' for any magic-filled game of ICRPG.
[5 of 5 Stars!]