Probably at some point all that time spent on Morrowind will eventually make your mind tired of the same first-person-action-adventure-rpg concept and Skyrim doesn′t renew the concept enough to break the monotomy.
This. Of course it also doesn't help that there are only 4 flavors of guild to choose from, each offering only 8 to 10 fully fleshed out quests.
I'm not saying this is bad per se, because instead of guilds and guild-quests they offer tons of side quests. But these stand alone quests don't break the feeling of 'been here, done that'.
So I too am starting to feel bored wnow that I've done the guilds and there isn't anything 'big' to uncover. The side quests and exploration has its charm but it is too much of the same. Even reviewers who started out with Oblivion acknowledged that Skyrim feels a bit too similar.
Even if these games are huge and take 4 years to make, they still can be blamed for unoriginality, just like games like CoD games are. Either reinvent the gameplay or put more storylines (guilds) in the game to keep it interesting.