http://www.gamesas.com/topic/1410023-relz-integration-the-stranded-light-a-true-rpg-quest-mod-experience/ is all about helping people, changing perceptions, and improving the world. There's some boss battles and dungeon crawling, but for the most part it also avoids forcing you to slaughter through hordes of living creatures to make the world better. Lot's of dialogue, choices/consequences, multiple solutions, character building, etc. all together it's 80+ quests, 5 new joinable guilds, a very long romance, a new town, and a number of other features you gradually gain over the course of the mod
Let's see, going off of thehttp://wiki.tesnexus.com/index.php/User:Deaths_soul/Recommended_Oblivion_Quest_Mods_List....
Kragenier's Death Quest: Is kind of a comedy mod, with references and jokes, and pop culture references galore, so.... probably not too depressing.
Tears of the Fiend didn't seem too depressing to me... I mean everything you mentioned were past events; and I'm pretty sure there is a possible happy ending
Spoiler Where everyone either lives or finds peace in their death
Windfall: Has a rebellion with at least one sad element, but it does have the potential for a positive ending
The Blackwood Company is a pretty evil mod with choices and consequences being a very big thing, so depending on your actions you may have to kill A LOT of people in the end.
Blood and Mud basically is meant to make Bravil more dark and gritty, so... probably don't want this one.
Daggerfall Memories: The Liberation of Cybiades is pretty straightforward: kill demonic creatures/gods to save the people.
Heart of The Dead has its fair share of twists and turns... a number of them sad and depressing, but overall it's pretty good and it's all about perspective, but yes... people that have dialogue do die.
The Lost Spires isn't too bad... There's only about one death and in the end you kill a great evil, so yeah it's a pretty standard affair
Malevolent is, pretty Malevolent... the premise of the mod is an armor forcing you to do stuff, and it does end in a cliffhanger that will likely never resolved.
Servant of the Dawn is evil, with it's share of evil things done.
The other mods I've either never played or are medium sized.
@Lobotomist: I think the mod you're thinking of is Moriarcis