If you're looking for a challenge...
I played a Vampire Illusionist with a self imposed level cap of 35, in robes and a hood with only Enchanting and Restoration to supplement it.
Purely passive build, make them fight themselves... but be sure to get the Vampire super perk in Resto.
If you're looking to have fun and still have somewhat of a challenge.
Use your shield as a weapon, and your free hand can supplement Shield Charge with any magic of your choosing.
I cannot stress how freaking awesome Shield Charge is...
I really don't like playing as a vampire, it never suited me, but an illusionist...maybe.
Spellsword/Battlemage. Heavily armored, Sword/Axe in one hand, Spell in the other... Best way to play in my opinion. If your a thieve type, Nightblade is a excellent choice, basically a thieve/assassin who uses magic.
I'm not playing as a Thief/Assassin again, already did it with my retired character. But a battlemage, maybe.
Pure merchant playthrough. Invest in Alchemy, Speech, Pickpocket, Smithing and Enchanting. Have only one goal - to make as much money as possible.
I'll probably play a travelling Khajiit merchant when I'm done with my second playthrough, sorta as a gag playthrough.
I guess I'll play as a 2H Nord Warrior who wields a battleaxe, but still indecisive as of yet. However, if they added combat on horseback, then I wouldn't mind creating a RIder of Rohan type character, and if they added spears... well that would just make my day.