The fact that the Emperor is Captain Picard is totally awesome.

Did you check out the Dark Brotherhood questline?

I was concentrating more on the Fighter's Guild and Mage's Guild ones, and then once I completed the main plot I wanted a break from it. I'll probably go back and tackle it and the expansion content at some point but I'd already invested something like 70 hours in the game and it was time for a change.

Ah, Oblivion. It's one of the few recent games that can still run on my machine, so it's good to take out for a wander every now and then.

In all honesty, I was never really all that "into" the storyline. It may just be my general disinterest in RPGs or my mainlining of nothing but straight FPS's for the past five years, but when I'm in Oblivion all I wanna do is run around as a lizard man and stab demons in the face (nice work if you can get it.)

This probably explains why, in the endgame when the Big Bad Wizard Dude was explaining the intricacies of his evil plan and his motivations, I listened for all of twenty seconds before deciding "right, I've had enough of this; time for stabbies!"

*enters discussion wearing an Elder Scrolls fanperson hat* *or Daedric helm*

It's a pity you gave up on Morrowind, I found the resolution of the main story quite interesting. It's one of the very few prophecy-driven stories I've ever seen that takes a moment to reflect on the nature of prophecy, and finishes on a satisfyingly ambiguous note in that regard.
(I admit I'm only about halfway through the main quest line in Oblivion, so I've yet to see how it compares.)

I'll echo Daniel and recommend the Dark Brotherhood quests. They're more creative and well-drawn-together than the others, with some very interesting twists and surprises. Plus, you get some really sweet goodies out of them, cool black armour aside.

Another comparison you could make is between the scope of both games. There are a great deal more factions, quests and items in Morrowind, and with less guidance offered the player has to explore and talk to people more than in Oblivion. I guess this is a good thing, as it forces you to engage a bit more with the fantabulously-constructed game environment. On the other, hand, it can also get rather tedious, particularly when the person you're looking for has accidentally fallen off a cliff or something.

P.S. I'm with you on the voice acting. Sean Bean makes my heart melt.

Well, luckily in one of the later Mage's Guild quest a totally legitimate kill-target counts as an innocent (I think maybe I was meant to listen to him cackle evilly before I hit him), so I've had the funky visit in my sleep and can start the Dark Brotherhood questline once I get back to the game. (My current plan is to finish the Fighter's Guild, do Knights of the Nine, have a slow spiral into villainy via the Brotherhood and the Thieves' Guild, then head for the Shivering Isles...)