It was pretty easy for me, but I was either playing on normal or adept. Could not deal with playing as a mage on harder difficulties. Having to cast shit like stone flesh and using wards was tedious - I just liked double-fireballing and summoning demora lords (TWO OF THEM!).
Playing as a vampire wasn't fun. I guess it could be if you were really low-level, but where I was with this mage (~30 maybe), it was a waste of time. Took way too long to kill the simplest things. Only useful application I found for vamp form was for quick traversal of terrain (flying over water especially).
Can't imagine anybody doing a pure mage playthrough on the hardest difficulty. I tried, and early on when you've only got magicka enough for a couple of spells and everything kills you in one hit? Naaaaah.
Anyway, if you haven't played Dawnguard yet and $20 is a lot of money to you, just wait.