I loved the spell mechanics of morrowind far more than the system in the later games.

It was broken and for the game to remain fun you had to restrict yourself from taking full advantage of the most broken elements.

But it also gave you almost unlimited freedom because you could use any spell in any way.

My favorite was a low powered levitation spell. At high power it allowed you to fly fast. At low power it allowed you to drift very very slowly.

Powerful, fast creature charging at you? Simply gift it weakly with the power of flight and laugh as it floats in the air unable to reach you at anything above a slow crawl.

For bonus cast it on a flying creature and it falls when the effect wears off, often hurting it.