It’s linear in the sense that you have a sequence of scenarios and the game is pretty much completed afterwards. You don’t have different factions, randomized starting positions or random events to add variety to your campaigns. It’s all pre-determined. Think of it as a story-driven singleplayer game which you play through once or twice and that’s it, rather than a game like SimCity or Civ.
The game is just too big for its own good imo.