Today I decided to play around a little with my level 50 Battlemage. To put things into perspective, both my destruction and one-handed skills are at 100, I have both of the augmented flame perks, and I have maxed out armsman and hack and slash (as well as having savage strike). I jumped into a falmer cave, and found that trying to kill them with just Incinerate ended up taking up just about my whole mana reserve (even with 28% reduction for destruction spells) to kill one enemy. My axe, on the other hand, took out baddies in 2-3 hits.
Now I really do hope Beth does something about this, at least in the next game (assuming there is one). Overall I love the magic system in Skyrim, but after a certain point (I want to say after level 40-ish?) it really does take a nose dive in comparison to melee. Hell, that would be a great thing to add to the DLC, some new spells, some kind of "nuke" spell. I figure Shivering Isles added spells to Oblivion, maybe this is something Beth should really consider.
PS: Before you suggest it, I'm console, no mods for me

