I basically made a destruction conjuration restoration caster, followed the Mage missions to completion, as well as the sidequest, and then went on with the main story. I leveled magicka:health in a 3:2 ratio and it works well. Got the Masters Destruction Robes, Morokei, a ring to reduce conjuration and galdur's amulet (haven't found anything better). My mage is around level 30 and gibs most ppl in my path.
I primarily use fire as it gets the most in terms of damage, i use frost and lightning equally at about half or less usage compared to fire. I conjure elementals to tank immediately and a undead for longer usage. The master level thrall spells are quite useful as it basically gives me 4 tanks to hide behind without the hero shouts. 1 elemental 1 undead 1 dog 1 groupie. I generally use ice form as a shout if i run out of magicka i just stand there and recharge while they thaw. Also wards are quite useful against spell casters and dragon breath.
I admit that my two-handed alt is fun and extremely easy to play but, I don't get the satisfaction of blasting people away with a kamehameha lightning storm, or walking into a enemy camp setting up a blizzard and watching them all die before they reach me. I can't say I don't die alot, but I can literally fight toe to toe with the dragon priest and win.