From what I read and see people saying both on forums and ingame, is that the mages guild ultimate is pretty weak and lackluster. It can be reflected and blocked. It just barely beats my crystal fragment dmg, and I can spam that one. For what it costs, its terrible...and very few people use it.
Id like to suggest a few things that might improve it. Increase the speed it travels, as in it will hit sooner after the initial sound. Make it unreflectable. Take away the AOE from it, make it single target and lower the cost considerably.
These are just my suggestions, and those might get me to start using it.
If you have any suggestions yourself, please share..
Altmer Sorceror, magicka
Bosmer Nightblade, stamina.
Imperial Templar, stamina
Redguard Warden, stamina