Morrowind was the best implementation of main quest vs. side quest in an open world game. A horrible fate for the world is clearly looming, but in a manner of years. More importantly you're a spy and told to build a cover identity as a freelancer.
The player is even provided with
a document detailing Dagoth Ur's long-term plans and explaining how the Sixth House has gradually expanded over decades:
...
Phase 1:
Secure Red Mountain against Tribunal intruders. Deny Tribunal access to the Heart, weakening the Temple while securing Red Mountain for the creation of Akulakhan. Keep the construction of Second Numidium a secret.
Phase 2:
Create passive servants in ever-widening circles around Red Mountain by broadcasting compulsions couched in dream imagery to susceptible subjects in their sleep. Establish a major operational base at Kogoruhn for further operations in the ash wastes. Establish smaller bases near small port villages and in lower-class waterfront districts in Vivec. Infiltrate and subvert smuggling syndicates. Recruit willing followers from disaffected populations, including the underworld, the poor, and rabid anti-Imperial activists.
Phase 3:
Expand from smaller bases to other towns and villages, and recruit and indoctrinate subjects made susceptible by dream sendings. Occupy abandoned towers and ruins, and train corrupted cultists as raiders and irregular troops. Identify, discredit, and decimate possible sources of political resistance.
Phase 4:
Use assassination and terror to weaken, distract, and disrupt the Legions and the Imperial bureaucracy, along with their Hlaalu sympathizers. Inspire popular uprisings of the native poor against the foreign rich and powerful. Summon Sleepers and Dreamers to Dagoth Ur to work on Second Numidium.
Dagoth Ur thinks on a large time scale -- for the most part, in the outside-of-time scale of the divine consciousness. He thinks that only obstacles of mythic scale are worth consideration. He believes he is fated to rule Morrowind, to free Morrowind of the Empire, and to become the new hard-loving Father of Morrowind. Given that perspective, the only opposing forces Dagoth Ur worries about are the Tribunal, the Daedra, the Emperor, and the Incarnate.
...
3E 400: Kogoruhn reoccupied by Dagoth Uthol and fortified as an advance base for Sixth House operations. Blight storms more frequent and widespread. Soul sickness spreads in regions close to Red Mountain.
3E 410: Sixth House bases founded near Gnaar Mok and in waterfront areas of Vivec. Sixth House operatives exploit smuggler organizations and communications to spread their influence among victims unbalanced by Dagoth Ur's dream sendings.
3E 415: Small cells of Sixth House cultists in every town in Vvardenfell. Larger Sixth House operations are concealed in remote dungeons where creatures are bred and cultists are trained for the coming struggle.
3E 417: Almalexia and Sotha Sil lose the artifacts Keening and Sunder to Dagoth Odros and Vemyn. Vivec rescues Almalexia and Sotha Sil, but failing to recover Keening and Sunder, the Tribunal retreat from Red Mountain in disorder. Surviving Buoyant Armiger companions know the Tribunal was forced to retreat, but do not know how serious a reversal the Tribunal has suffered. The Three Tribunes return to their respective capitals and continue to perform their ritual functions. The Tribunes continue to grow weaker without access to the Heart, and because of resources required to support the Ghostfence. The inner circle of the Temple priesthood has begun to suspect the Tribunes have suffered seriously from wounds and demoralization in the wake of reverses at Red Mountain, but do not recognize the scale of the problem.
3E 426-427: Campaign of Sixth House assassinations of prominent Imperial citizens and Hlaalu Imperial sympathizers. Sudden increase in number and seriousness of attacks by cultists and victims deranged by soul sickness.
...
