There are several reasons why magic in Skyrim just sort of svcks.
Destruction is really not viable late in the game, especially on higher difficulties. There simply is not enough magicka in the world to kill things with these spells. Rather than becoming more efficient when you get to higher end destruction spells it gets less and less efficient. Sure, impact is nastily powerful, being able to stagger enemies on demand is very potent, but it really doesn't help once every other encounter consists of 3+ enemies that all require more magicka to kill than your character can have.
Illusion is next to worthless. Half the enemies in the game can't even be affected by illusion spells until you hit 100 in it. Since the spells are restricted by level of creature they can afffect, and only animals and humanoids ever get a bonus to that level even if you get the perk that lets you cast illusion spells on anything those things will most likely outlevel your spells. Bethesda got this absolutely backwards. Why create a spell school that can placate or enrage weak enemies that you can simply sweep out of your way anyways? What I need these spells to do is help me defeat the powerful foes - but the game is built so that the powerful enemies can't be affected at all.
Paralysis has the same issue. The reason Paralysis was good in Morrowind and Oblivion was because if you ran into an enemy that was much more powerful than you you could paralyze them to even the odds. Now the game simply states that powerful foes can't be paralyzed. Why would I want to paralyze a weak enemy though? I can just kill them anyways.
The whole magicka regen through perks and wearing robes thing... Not really useful, since in combat your regen bonuses shut down. Yea, that's right. When you're in combat you lose the benefit from your gear if it's enchanted with stuff that would make playing a magic wielder actually possible. For all practical purposes, the huge penulties you take on yourself by wearing robes instead of armor have no real benefit outside of some convenience in between fights. In a fight armor trumps robes even if you are a pure mage, since regen will be identical.
Enchantment is more useful to any warrior than a mage. Staves don't benefit from any weapon skill, and even if they did - what the heck, I feel like its morrowind all over again where your only hope of killing something with offisive spells was to use an item that was enchanted with offensive spells.
Alteration is just as annoying and bland as in the other games. Nobody wants to recast a shield spell every minute, especially if it knocks a gargantuan chunk of Magicka off your bar which is insufficient to fuel combat magicks in the first place. This is even more annoying now that you need to cast in combat to level the skill.
Restoration is kind of worthless too. You can go the whole game without ever using any other effect then Heal, which you have from level 1. You don't really need any of the other Restoration spells. The idea behind the new Absorbs is cool, but the implementation is clashing with the realities of the magic system. In a system where you never ever have enough magicka in the first place the whole idea of fueling defenses with even more magicka just becomes sort of ridiculous.
I would really like to see some tweaking of this stuff. This game would simply be more enjoyable if it wasn't such

i dont get why they removed open lock spells, though it only seems useful for shield spells. And the perks are more of defensive.
