IMHO, one of the big Problems with Magic in Skyrim is the perk tree, especially for destruction, as well as some really odd design decisions with how some skills affect leveled enemies.
The Novice, Apprentice, Adept, Expert, Master perk tree in Skyrim is just completely pointless. Spells already get cheaper as your respective skill goes up. For some reason, Bethesda put in two systems that do the same, when you could have used those perk points for something that is actually interesting.
Overall, destruction perks are boring: Dual casting is inefficient and practically useless, if you don't have the Impact perk, which is overpowered because it is not based on a formula. Out of 17 perk points, 11 are just damage or efficiency increases. None offers any reason to switch or chain spells. Of the remaining perks, Rune Master is gimmicky (could be tied to skill instead), Intense Flames and Deep Frost are very situational. Disintegrate seems cool, but in reality it's just another damage buff. Basically, Destruction magic is really boring. Oh and the Master level destruction spells are very situational, too.
Added to that are Conjurations summons that aren't leveled, meaning that they will be OP when you get them, and useless later. Several different raise dead spells that all do the same thing. Also several different Illusion spells for each kind that all do the same thing. A paralyze spell that simply paralizes anything that isn't immune isn't really the best idea, either.
The Mage Armor perks are necessary if you want to play a pure mage, but mean that most of the enchanted items you find, including important artifacts like Dragon Masks, are off-limits for you. Until you get the Master level Alteration spell Dragonhide, which offers 80% damage reduction no matter your perks, which makes Mage Armor completely redundant and thereby also removes any limitation on what you can wear.