Necromancers' guild was something Oblivion lacked, especially because they made an appearance in the game. What guild I thought was needed was a hunter guild. I also thought fighters guild had the best storyline. I don't want to spoil anything about the storyline but if you've ever played AND BEATEN the fighters guild then you know what I mean. :foodndrink:
The fighter's guild had a good story, but imo it had some of the worst missions. On subsequent playthroughs I just couldn't stomach the first half-dozen missions.
Necromancer's guild imo would be awesome, we need an evil mage faction. First off, the spells you could learn from them would be awesome. Secondly, the missions would be interesting, like "kill this isolated village, raise the corpses as skeletons for mannimarco's army.