Being a mage is really fun. Although, it is necessary to have a mod that increases the power of destruction spells! The vanilla version of these were, well...not powerful at all.
But be careful, it increases the damage for ALL characters in the game, not just your own. So be careful when taking on a castle of necromancers
Not singling Vault Demon out, but I've seen this all over these boards and I respectfully disagree.
My mileage has varied considerably. When I decided to try a pure mage, I prepared by downloadng all sorts of mods that scaled destruction, etc. but wanted to try it vanilla at first just for comparison. I never ended up installing any "balancing" mods
I'm playing on adept, but with the appropriate destruction damage perks and reduction perks in Destro, Alteration and Conjuration, I have had little trouble dealing with most situations. Currently level 39
Admittedly, I'm playing a Breton and I snagged Atronach Stone at about level 20. I
did grab a mod that lets me wear hoods and circlets together, but essentially that saves me from having to drink one extra potion per combat or so.
I haven't had to spam potions.
I've only had a follower through Bleak Falls (Sven- mostly just to draw aggro), Labyrinthan and Blackreach (mostly as a pack mule).
I have relied more heavily on shouts than I did with my other characters- mostly Ice Form for those "Oh, Censored!" moments.
Impact Perk is a must (lots of folks complain that stun-locking with it is OP, but shield bash does the same thing and apparently that's O.K.).
I think magic is just fine, just play like a mage. Mages are squishy by nature. Don't expect to go toe to toe with a Greatsword-wielding Bandit Chief. Mage Armor isn't armor- it's a contingency plan.
I'm sure Expert or Master difficulty changes things considerably, but I'm having fun with this character and I have nothing to prove by taking the difficulty out of my comfort zone.