Magic was infinitely better in Oblivion. First and foremost you could enchant your gear with Shield to make unbreakable cloth armor that was better than any actual armor that you needed to repair after every other hit at high lvls.
Since repair isn't a thing in Skyrim you might say its a moot point, but as I think all the armor in Skyrim looks like ass I'd rather just enchant my clothes instead of either having to cast Enonyflesh over and over and over, or abuse the hell out of smithing to make Steel Plate or Scaled Armor get to the cap.
In Oblivion I didn't have to go out of my way to find spell books/level up high enough to be able to even buy them. I just went to the Mage's Guild and made what I was optimally capable of using at my level and scaled up as I needed to.
I also was able to make SO MANY different spells with effects from multiple schools of magic. My favorite being a freezing fog aoe that paralyzed briefly. It wasn't nearly as OP as the tri-elemental spells with a one second drain health that could one shot practically anything though.
In Skyrim, there are far fewer spell effects and you are limited to very few actual spells. Of those, most are only slightly different from each other and all of them do really sad damage at high levels since they are hard capped and only slightly able to be augmented.
To compensate you are supposed to spam the crap out of them with impact or use all the schools of magic heavily to even the odds that being pure destruction would leave you with. Too many enemies? Better have them kill each other with a rage spell, or if they are too high a level for that you had better summon a deadra. They still coming? Better hope you killed a few to raise up, or that you still have enough magicka to spam destruction spells/paralyze/bound weapon them to death.
Having to fall back to using bound weapons because you have run out of magicka becomes far too prevalent unless you take magicka every level up/stack mage enchants on gear.
At that point you can just abuse enchanting to get cost free spells in 2 schools and get to spam them freely.
You still won't be killing anything any faster than if you just picked up a dagger and went apeshit, or a bow. You will also not have to spread 2 dozen perks across 5 trees just to be competent, and so on.
In Oblivion you also don't have to forgo your shield/weapon to cast. You can't break the game to get free casting either, and wearing armor reduced spell effectiveness in one of the last fits of actual balance Bethesda decided to employ in the series.
But there is one way in which Skyrim beats Oblivion magic. You don't get to have a pov kill cam of your ice spear flying and slamming into a deer or mudcrab. Which is about the only things you will be able to kill with it due to ice damage in both games being HEAVILY resisted by pretty much half the enemies.
Seriously I love ice magic, yet feel required to use fire because of balance issues. You'd think frost resist would only apply to spells like frostbite and ice storm, not getting impaled with ice spears. If anything that should be doing physical damage, and could fulfill that niche in a pure caster's repertoire instead of having to rely on summons/bound weapons.
I don't even bother with the master level spells in Skyrim, or the wall/cloak spells. They are cost inefficient, and the cloak spells cancel if you summon anything.
Even so, no matter which game's magic you prefer they are both better than TES melee combat by several orders of magnitude.
Archery I find to be the most effective/fun but rarely use it due to having to find my arrows/bound arrows never cleaning so it eventually causes massive lag.
I also prefer Oblivion in pretty much every way aside from the leveling mechanics. It has better looking gear, more enemy variety, bigger cities, and you can make way better looking characters. Sure the Oblivion NPCs look kind of goofy, but at least they don't all look like dirty meth addicts. I prefer Bretons, but the options in Skyrim are limited and all come with giant creased foreheads.
