This is the second expansion to Dune: Imperium. It adds two new tracks to earn resources and VPs, as well as a new card acquisition approach and a batch of new cards, which improves the DBG elements a little bit (imo the best part fo this expansion).
While Rise of Ix is a must-buy that feels like part of the base game (you can include it even for your first game), Immortality is more like an expansion, which adds variety. On the other hand, Immortality also make the game slightly more complex due to the extra elements.
I recommand it to DI funs with good familiarity with Ix, otherwise please buy Ix first, because DI+Ix already feel very complete.

Played it solo once, twice with two players (and the app as the third player) and once with three players. Solo and two player very relaxed and good to learn the basics; three player game got very frantic! The intrigue cards are ridiculous and flipped the game totally in endgame stage!
Looking foreward to play again!