1) Magicka regeneration rate during battle is 3%, so even if you had +200% regen rate bonuses you would only have 9% in battle. This is ridiculous, not sure why this was added to be honest, I can understand health being low in battle but I think stamina and magicka should be at 75% or 50%. Especially magicka considering it's a pure mages only weapon, forcing mages to use potions to continue casting.

2) Alteration armor is decent, and usable, I use ebonyflesh dual casted which gives me 300 armor rating for just over 3 mins (with the duration perk and mage armor x3), or dragonhide which gives me 80% damage resist (the max achievable with armor) for 99 seconds. But I think they could have made them last longer, so they could make ebonyflesh last for 6-10 mins and dragonhide 2-3 mins, just to make it more usable compared to armor. Also I think the mage armor perk should increase your armor rating with flesh spells by x2, x3 then x4 with increasing perks. Instead of x2, x2.5 and x3, just to make it more useful compared to armor. Some more alteration perks for not wearing armor should be added also, maybe 30% chance to ignore damage or half stamina usage.

3) Unique enchantments on clothing aren't good enough, the arch mage robes give you +50 magicka, +100% regen rate and +15% fortify spell consumption, taking up the head slot and chest slot. You can enchant your own armor with 4 enchantments for the chest and the head which are more useful than the arch mage robes. With master robes of [magic school], you get 150% magicka rate, which would be useful if not for my first point (regen rate) making is pretty useless in battle. The other effect of the master robes of [magic school] is the % reduction of magicka cost, which can be beaten by enchanting your own clothes, so maybe they could have a fortify effect of magnitude +35% to make them more powerful.

4) Master spells ARE good, and usable, it's just the charge time that lets them down (if you stagger from an enemy attack it will break the charge to). So I think there should be a quest available, when you have all the master spells, in the college of winterhold that allows you to reduce the charge time of master spells, and staggering doesn't break the charge. Otherwise than that, they do a decent amount of damage/effect, for example blizzard/mass paralyse combined with become ethereal/invisibility will allow you to charge right next to the enemy and pretty much destroy them.

5) Destruction damage, could be better at high levels as a lot of people have said, I don't think damage scaling is the answer. Maybe instead they could improve the perks available, instead of +25% then +50% damage for each element, you could have +40% damage then +80% and then 120% damage (destruction requirements being 40, 60 and 80).

6) Illusion is powerful, and when dual casted with all the perks in the right illusion tree, you can use the basic fury/frenzy/calm/fear spells on anything that doesn't resist illusion, even at level 70+, probably at the highest level due to enemies stopping scaling. They could have added some more manipulation effects to make it a bit more interesting though. Maybe a stop effect where they just stand still or an effect where they attack themselves, just some ideas.

7) Conjuration can be very powerful, the last perk can allow you to have 2 dremora lords, or 2 thralls/atronachs. Dead thrall only works on enemies up to level 40 though, which maybe could be higher for use at very high levels.

8) Can't really say much for restoration as I don't bother with it, would rather use alchemy. But I've heard the repel undead spells can be useful, plus the master spell can affect the highest level undead (draugr deathlords).

9) Minor problem I have would be the lack of unenchanted hoods that look half decent, maybe the option to unchant any apparel even if you know the enchantment or the enchantment can't be learned. So you can do what you want with any apparel.

Well these are just some ideas/opinions I have, any thoughts?