I think they are probably a bit shorter. I just generally felt that each guild had less missions before you reached the top. The Mages Guild seemed especially short and ended rather abruptly. The thieves guild takes a while in Skyrim but that's because you need to do lots of the minor missions before you can be guild leader. The actual questline is relatively short.
Having said that, they did also have the StormCloak vs Imperials questline which Oblivion didn't have and I do seem to get more minor/random quests due to the new quest system they have in place.
Yeah it's a shame the mage guild quest line was so short, that one was the most interesting of the lot. The Stormcloak vs Imperials was the most disappointing one, capture the fort missions were very poorly executed. The daedric armor ones were great in Skyrim, although there were a couple boring ones too. Skyrim has more minor quests and random quests, but they're all rather straightforward fetch or kill quests.
Marketh and Solitude were my favorites as well, beautiful cities. However they still felt very small. There was no main city like the imperial city in Oblivion. (loved the arena challenges) Skyrim has more towns, but the 5 structure strong holds were very repetitive with the same houses and exact same inn everywhere. (There's twice as many guards walking around then there are people living in each village)
The dungeons have been vastly improved in Skyrim, Bthardzam was my favorite. It's a shame Blackreach wasn't utilized for more quests instead of going into the caves all the time. I would expect that the Winterhold college would be very interested in that place.