Originally Posted by dwette
I'm undecided wether I want to spend the money for the Shivering Isles expansion.
I really enjoyed the Mehrunes Razor quest. It's only about $3.00, is engaging, and has some really cool magic stuff. Make sure you... [/spoiler]
Shivering isles has a few different quest. Plus the creatures and environment are significantly different. The dungeons have a few new twists to them, too.
Knights of the nine is mostly built around puzzle oriented challenges.
As for the prisoner in the Mehrunes Razor quest, there are several ways to handle it. Releasing him and following him discretely will lead to an interesting outcome more often than not. (Just not always.)
Beyond the standard quests, though, there is room for your own quests if you're so inclined.
A couple of possibilities:
There is a set of Four High-end Magic Rings (Storm, Flame, Frost, Vitality) that offer 100% elemental protection.
If you're a high-level alchemist, you can try to get a full set of Master-level gear.
(You only need three--plus one expert-level aparatus--to make the best potions and poisons, but it is a major challenge to get all four.)
If you haven't finished the Main quest, you could try to get one of each of the Transcendant Sigil stones. (30 different types.)
If you haven't finished the thieves quest, you can try to find a way to finish the quest but keep the boots of Springheel Jak. Doable but hardly trivial.
On Knights of the nine, try to beat the big Bad without losing a single one of your Knights.
And, of course, you could try to build up your character to full perfection; 100 on everything, or try to play through as a completely different character with a completely different MO.
Remember, Oblivion is a sandbox; what you get from it is a function of what you put in. Its all a matter of what interests you.
If you have Shivering Isles you can go questing for Amber and Madness ore; it takes a lot to build a full set of armor and weapons, even more to get a full set of the *magical* versions.