Would you want to have actual spells rather than spell effects? Instead of having spells that are more or less all the same (fire damage, frost, electric etc) have fewer spells with unique effects like boil their blood or turn their underwear to wood? Magic in Oblivion just seemed another kind of gun to me, just like in Borderlands...
My opinion
Scripted spells. Just look at the PC mod Midas Magic, with scripting you can make unbelievable spells, and I'm sure Bethesda will add some if not a bunch.
And you can combine effects to create awesome spells, in vanilla Oblivion there were no freezing spells so I combined paralysis with frost and armor desentragation (typo? I cant spell this
) to create a freezing spell that stopped the enemy while applying frost damage while making the enemy vulnerable to my attacks.