I kind of like that the mages guild has dissolved into two rival organizations. It's a bit of a throwback to Morrowind - in MW, you had the Mages Guild and the Telvanni Wizards, you had the thieves guild and the morag tong, you had the Temple and the Tribunal. And you had the 3 Great Houses (ok, technically 5 Great Houses, 2 of the Houses were, in Lore, not present on Vvardenfell - only on the mainland, which you never really visit (except for the capital city in the 'Tribunal' expansion pack).
It gave you some choice - I thought it kind of stank, from an RP perspective, that in Oblivion, the mages' guild had a pseudo-monopoly on magic - you could get *some* spells (mostly restoration and conjuration) from the Temple priests, but unless you bought the Frostcrag Spire add-on, you couldn't make spells or enchantments without joining the mages guild, and you pretty much had to buy most spell types from the mages guild.
The problem with that, for me, is that I played through a few times, and one a couple of the characters, it made sense that they'd join up with the mages guild. But, I wanted to play an arcane assassin type character - basically, stealth, archery, short blade, light armor, alchemy for poisons and heals, and I allowed myself one school of magic - Illusion, to sort of 'complete' the character concept.
The problem was, the rigidity of how things were setup in Oblivion meant that my thieves guild/dark brotherhood chaotic evil character had to be part of the goody-goody mages guild to get access to illusion spells, and the altars.
Now, for such a character, it should be *harder*, more expensive, etc to get access to those services without the mages guild (since they are sort of the officially sanctioned 'guardians of magic' for the Empire) - but good game world design would allow such characters a challenging, but alternate path to get such services.
Anyhow, if TES V: Skyrim goes back to more of a Morrowind direction, where you have more choices about organizations you join, I think that would be pretty awesome.