I haven't gotten my mage very far, atm only lvl 28 but i gotta say, up until lvl 17-18 being a mage is quite harder than being a dual-wielding slicing machine. But things are starting to even out now even though my gear is shite compared to what i had on my warrior at that level. Thing is, there is more to being a mage than firebolts. Personally, i don't use alteration or illusion much, but conjuration in conjunction with destruction can be very good. Just summon an atronarch to do the tanking and dual cast fireballs, things drop like flies and en masse since the AoE from fireball is really nice.