I didn't finish the College questline because I was playing a DiD character and he ended up dying during one of the quests but at that point I was having quite some fun completing the guild's quests and it didn't feel dull at all. Without giving anything away I can say I was going after a certain staff when I died.
But then again I take my time and I don't rush things.
Again, Captain, we're not talking about how many hours it took to do the questlines (heck, I only got around to hitting Solitude for the MQ in the thirties, and only finished it after level 50).
We're talking about number of quests.
As I mentioned, the Companions questline - possibly bugged - didn't make/let me do more than one random filler quest in between the main quests. I was a trusted member of the Circle almost immediately after joining, and the whole questline was done within six or so quests. Doesn't matter if I rushed through them in an hour, or if I spread them out over 60 hours of other stuff - the questline itself was
short.