I currently own Oblivion but without the Knight of the Nine and Shivering Isle and run the game on a fairly old pc. I must say the graphics although awesome are no where near on full spec. Despite it's beauty and detail I am starting to find that I am getting bored with just the simple hack and slash. One reason could be that I do not get very far in the single player main campaign because of real life taking me away from the game then when I come back I want to play a different character.
But! On Friday I have a new pc coming and intend to start playing again and I wanted to know if there were any mods that added more depth to the game in the same way there are great mods for BGII such as extra quests with deep storylines, romanceable npc's, strongholds...etc. I've had a quick look at the mods and I've so far just seen custom items/clothing, graphical tweaks and naked female models. Maybe I'm missing the better mods or is that all that there is so far?
Also I wanted to know if it's worth getting shivering isles/knights of the nine because I will most likely play a evil character (I find good guys overplayed by myself) and simply want to know if these add-ons are just hack and slash or is there some more depth to it than that. If anyone has any tips on making the game more interesting or would like to point out what I may be doing wrong in my approach to the game then feel free to rip!

Thanks in advance.