Dragon Shouts.
sounds weird but I'll hold off making any comment until I play it...
...however. I remember playing a game not too long ago (forgot the name) but you had to memorize odd shapes and wriggle the mouse in specific patterns to caste spells.
I always got it wrong and it completely ruined my enjoyment of the game. (I know others loved it).
I hope these 'shouts' are more manageable.
This game you played before is called Arx Fatalis, it has a very interesting spell mechanic, kinda frustrating sometimes when you wanted a fast paced action. Though you could always check the runes and patterns in your spellbook as well stack up to 3 spells for a later use, not requiring you to cast the runes each time.
Dragon Shouts seems like a very interesting and powerful mechanic, it should make the magic and combat very fast-paced and visceral. Just like Oblivion and the magic system in it, you should be able to select a single shout in the character menu to ready it to be used with a press of a single key or button. Charging the shouts should only give a more powerful effect, and you won't have to memorize each timing and word so you can use a specific shout, after all this would become very annoying.