Let me clarify: when I say 'failure' I'm not talking about sales or content - I'm talking about the overall direction of the game and its main mechanics.
Don't get me wrong: Civ 6 does some things really well; e.g.
- City planning and districts;
- Tech/Civic trees;
- Governments and policies;
- The Climate Change mechanic is good;
- Civ and Leader abilities;
There are, in my view, many things that they got wrong. The reasons why I believe they got them wrong was believe they had a vision for the game and were committed to adhering to that vision. Here some things I believe they got wrong:
- Diplomacy and World Congress;
- Agendas and Trade;
- War, military and combat;
- Unique units, buildings and improvements;
- Graphics and leader art.
There were many things they could've retained from previous iterations of Civilization that were really good. For e.g. corporations and health was a great opportunity in the base game.
I suspect, and this is my opinion, that Civilization 7 would aim to return to some of the mechanics that were in Civ 4 or earlier iterations, whilst aiming to incorporate some successful ones, such as Climate Change.