At the end of a long campaign, my player group's PCs ascended to immortality. Since I had a copy of the Immortals boxed set lying around, I attempted to continue the campaign using those rules, and almost immediately threw in the towel.
In my opinion, there were many confusing elements of that rule set, but some of the biggest gaps related to the fundamental structure of the campaign, such as:
- What are the goals and constraints of the characters?
- What are scales of time and space involved?
- How does a campaign narrative work, if the players might decide at any moment to take a century of downtime to touch-up their home demi-planes?
The published module I had at the time didn't clarify most of these issues; it assumed a lot of railroading of PCs through actions that they did not seem to have a motivation to engage in, and "challenges" that they might as well avoid (wandering monster in the Astral plane, a lich and his entourage: why would they engage in any way with wandering monsters at this point?).
How were Immortal-level campaigns run, in practice?