I've been jumping all over each guild quest line, have yet to fully complete all the tasks of any one guild, partly because I hear some issues with some of the quests breaking, so I am more or less just waiting for the patch that will hopefully address them, I fear also, that the patch may require recreation of characters.
As far as the Oblivion Planes, I wish they had made them more varied, after the first 3 or so, you start feeling a bit too much like repeats, however, the sigil stones at least make it somewhat worthwhile. (I have found if you activate the sigil stone multiple times when you goto grab it, you can end up with several stones from the one plane (bug), sometimes it doesn't work though, and when I found the bug, I restarted and did not exploit it the next time around, I don't like to cheat the first time through, if at all, to me cheating is a waste of 60 bucks!).
It also seems they stripped alot of the content promised in the demo at E3, in order to sell them bit by bit (to be fair, this may be just the cynic in me).
And _good_ free content/mods (adding meshes with havoc attributes without having to clone existing objects is not really possible yet) from the mod community is being held up because Beth did not release the nif exporter for it yet (no doubt to prevent the community from releasing free versions of Horse Armour, Orrery, etc. before Beth can make a buck (which, btw, I do NOT blame them for, I am just mentioning it)).
Overall, the way I see it, is that Beth purposly left ALOT open (most of the land is unused) to give the community room to add ALOT of content, which I think is really awesome of them, for them to release a contruction set at all makes all the bugs, not so bad.
Enjoy!