Skyrim's magic is pretty bad because it doesn't scale well (basically, it sucks). You need to work on it a lot to keep it useful, or exploit certain things (Impact). And this requires full-time magery. And i do not like pure classes really. So i'm really talking only for myself but...
Pure mage is fun until i realize i'm sticking to one thing only because i can't do anything but to stick to one thing, for various reason (mana limits, need to advance offensive skills quickly, why waste mana on armor spell when i day if someone gets to hit me anyway). And it also stops being fun when i realize i can't afford more advanced spells, and i can't obtain money (by killing and looting things, i don't like crafting aside from occasional use) effectively without those advanced spells... Unless i start exploiting the system, which won't feel like being a mage.
Mage-hybrids do not work well in Skyrim either, magic is cumbersome due to constant menu use even with hotkeys (and i play with 360 controller). Melee doesn't combine with magic as i explained earlier, it is impossible to aim fast (using magic slows down aiming with 360 controller, no idea about KB/M) and prevents fast melee attacks.
Shouting works well due to their own button but is hampered by long cooldowns and not being a skill, it doesn't advance my character.
Illusion magic: Powerful once trained, to the point of being a game-breaker. Nearly no enemy can resist you, or detect you (especially if combine with sneaking). And then you see a dragon and your magic is utterly pointless. Unless i have something else with Illusion, which kind of defeats the point of Illusion magic in the first place (avoiding combat and making enemies fight each other, utterly pointless in support role because if you use melee/archery, you want to use your weapons as much as possible for highest skill-gain).
Runes: Can't use them right away, weak and AFAIK they don't benefit from perks aside from Rune Mastery, don't scale at all, mana-inefficient. Much more effective to blast my enemies with direct attacks and exploit terrain to stay out of reach. Rune Mastery is a waste of perk, for a mere 3 spells (unless you count the few runes added by Dragonborn, which are in other schools...).
A note on staves: Who the fuck thought it was a good idea not to have them increase skill of the relevant school? Who the fuck thought it was a good idea not to have them benefit from perks? Who the fuck though it was good idea to make Illusion/Conjuration staves so damn useless due to their low magnitude (and Conjuration and Restoration spells also suffer from this low magnitude issue as they're not boosted by dual-casting unlike Illusion spells, only duration).
Notes on Oblivion and Morrowind magic:
Oblivion's magic system had the advantage of quick casting, making it easy to combine with other play-styles, but the armor effectiveness and limited access to spells without enough skill (or Arcane University or fast travel to city guild halls) killed it for me. Also the magic was kind of exploitative in nature (weakness stacking on enemies) though it was powerful, after long training, which is a no-no for me as i want to feel good right away (Skyrim's magic does sort-of do this).
Morrowind magic was also powerful, aside from high-end enemies having Reflect... And it also suffers from casting stance, long casting times, failure chance... Also looked boring and terrible. Code Patch helps with addition of quick-cast key.
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Still, despite all my above complaints, i'm planning a hybrid mage-stealth character at the moment. Alteration, Illusion, Sneak, Pickpocket, Archery.
I don't think it's going to work well though, going to require slow, methodical playing to keep skills up (Calm enemies and then kill them anyway).
In theory the build should have good synergy, Illusion providing quiet casting and being crowd control and boosting sneaking, Alteration providing armor and magic-resistance and utility for sneaking, sneaking and archery giving me potent killing power, and Pickpocket being there just for fun and roleplaying.
