I've been playing a destruction mage without doing any enchanting, and I found the cost of master level destruction spells to be pretty reasonable. It's not useless. You can't spam it, but I have enough magicka to cast Fire Storm, a nice AoE damage spell, and Blizzard, a lingering AoE spell with pretty large effective area, 4-5 times. And lightning storm is very cheap and has very high damage output, like a supercharged concentration spell. It has very high damage per magicka. The drawback is the wind up time and the fact that you can't move while mowing down everything in your sight.

Honestly the only master level spells I've not found to be borderline useless are mass paralysis, & only if I use it as an opener while invisible, the thrall spells, & guardian circle.

Thrall spells: All worth it.

The restoration spells are good against undead. Dawnbreaker on a one hand master achieves the same thing.

Destruction: Lightning storm is fun & pretty... but not as great as people make it sound. In my experience you can achieve higher damage per second dual casting thunderbolts. Maybe its not higher, it just feels that way since I can still MOVE meaning I can walk backward increasing the amount of time it takes my enemy to reach me.... plus it staggers. Thunderbolt > Lightning Storm

I did find one fun use for lightning storm. Doing civil war quests at level 70. The poor Imperials were so outclassed they were turned to ashes almost instantly when the lightning beam hit them. I would get in a high place and rain down death turning everyone to ash. I felt like one of the tripods in war of the worlds. Other than that... useless.

Firestorm and blizzard are just horrible. Fireball > Firestorm because of range/mobility/cast time/spell cost. Sad since we are comparing a adept level spell to a master level spell.

Illusion: Fun on occasion, but the adept/expert spells still seem more useful. These are novelty spells.

Alteration: eh....

The problem I have with the master level spells (specifically destruction) is that if you want to use them you have to forfeit using companions basically. The long charge might not be so bad if I could have a companion attack head first while I sit back and ready my spell, but all the master level destruction spells are pretty much impossible to cast (maybe Lighting Storm) without hurting your companion and inadvertently killing them.

Fixed that for you.

Idk if anyone else has had this problem but also casting firestorm and icestorm sometimes ive taken damage from them. You have to quickly (funny joke) use them and then run away. Which makes them pointless b/c then if the enemy wasnt instantly killed they chase after you and get away from the blast radius anyways.

I think I can clear any dungeon just using destruction master spells and shouts. I think many of the destruction users would be able to do this as well. It may not be the easiest way to clear a dungeon, but I think it's definitely possible.

They are costly to cast if you're not using enchanted items, but when you put perks into enchanting you can eventually put 2 enchantments on the same item.

For example, I wear a circlet, necklace, and ring that reduce the cost of both Alteration and Destruction spells by 29% each, and a Master-level robe for each type of magic. I do the same with other combinations I use frequently together, like Destruction and Restoration.

Absoluetly! Flame Thrall is your friend.

I don't mind the magicka cost, i just hate the fact that they can be interrupted. I can't remember one time i ever casted a master destruction spell when there were 5 or 6 draugr surrounding me because i was always interrupted doing it.

I'm not the only one who did this I see... Even better after you loot his body for his clothes and have him run around half naked.

Thats why you enchant your gear for cost reduction. There is a reason for these types of enchantments being available.