HEADS UP: The following post may contain very mild spoilers.
I feel like they really missed a good opportunity with the generic quests. I felt like in Oblivion, since they had to voice every quest and make each one unique, they were limited in a big way with how long they could make the quest lines. With Skyrim, they have an awesome tool, with the generic quests. I really think they should have done more to force you to do a guild's side quests to continue with the main quest of it. I mean, I found out that Keening was in this game online, and so I went and did a short series of quests for a guy at the College, and I feel like it could have been used to pad out my time in the main quest. Like, the Archmage would say something like "I know that the Psijics want you to do this, but I really feel like you don't have enough experience as a mage yet. Take care of some College business and I'll allow you to pursue this." Then you have to actually go ask somebody for their mini quest line. With the Dark Brotherhood, I feel that there weren't enough actual assassinations. I get that the main story is rebuilding the Brotherhood, but aside from the boring contracts and the contract leading up to the final mission, you kill like 3 people. I think it would have been way better to build it up a little more before naming you Listener. The Companions could have you being forced to clear out a few dungeons or something like that. The Thieves Guild did pretty well with the amount of missions you get, but I feel like in between big missions you should have been forced to do a few generic ones. I mean, I ended up doing some 40 generic missions in a row after completing the quest line just to become Guild Master. Not a very climactic ending.
Obviously on top of this you could have skill requirements, so I have to actually know how to cast magic to be Archmage.