There were both good and bad aspects to MW's system, and good and bad points to OB's as well.
Morrowind provided a deeper "pool", so you could toss a few powerful spells in a row without having to "stall" until it regenerated. Unfortunately, with NO regeneration, you were more or less "done" when the pool ran dry, unless you brought potions along. I liked the "strategic" aspect of conserving your magicka for "important" moments, but the total lack of natural regen was the pits.
I modded in a very gradual magicka regeneration, about 10% of OB's rate or less, which worked very well because of the deeper reservoir. It was there when it mattered, but you had to keep it in mind and not "waste" it.
Oblivion used a shallow puddle instead of a "pool", but had a solid stream feeding it. You could only throw one or two "good" spells, or a handful of "irritants", and then had to buy time until it recharged, which happened relatively quickly. It took the "thought" out of playing a magic-user, and just turned your wizard into a "barbarian with spells instead of a sword". Rather than watching your fatigue bar from time to time, you had to keep an occasional eye on your magicka level instead. Ihad one character with a couple of spells which he could technically cast, but without sufficient magicka to do so.
Giving a deeper "pool" than OB, but with a GRADUAL regen, would be the best of both, in my opinion. The regen rate for enchantments in MW was excellent: gradual enough that you had to be cautious about using them, but fast enough that you didn't have to constantly recharge them with soulgems if you weren't using them continuously.
Slower regen, YES, but balance that with more reserves, PLEASE.
Actually to supplement this idea, slower regen, with only slightly larger reserves. However, a player should be able to 'store' additional magicka above their normal reserves. Actions like drawing power from a magickal well would give you raw magicka, instead of a temporary fortify magicka effect. The caveat to this raw magicka is that once it is expended, it is gone for good. This would be a good way to increase the amount of energy for a battle, but would also encourage tactical conservation, as this 'bonus' magicka would not regenerate. This could be a backup reserve for when your personal magicka runs out. Absorb magicka spells could be more useful if you could store the unused energy for a future fight.
I always liked the idea perpetrated in the Eragon books with precious stones being able to store magickal energy. So, having a high quality ring or amulet with a stone, a mage would be able to store more additional magicka, while lower quality jewelry would hold less additional energy. Also, if you knew you weren't goning to be in a fight anytime soon, you could store your magicka away for future use.
All this could be implemented as a perk, instead of a default ability. Perhaps ability to store magicka could be related to Willpower, with lower levels only storing part of what they are absorbing.