I don't mind the idea of a resource that runs out. In pretty much every popular strategy game out there (Starcraft 2 for example), when you run out of a resource...well too bad buddy, go mine some more.
In AI War I feel like we've been coddled a little too much in this category. The fact that we're merging Metal and Crystal together after all these years, because they've become so interchangeable, is proof of that. Just like in any other strategy game (or in real-life strategy), if you're not tailoring your production and your army based on the resources available to you, then you're doing it wrong.
I do disagree with this. AI War is largely centered around you setting the pace, you claiming territory when you see a resource you really really need. Why? Because while m/c are infinite in supply, your knowledge, overall tech, and map control are dictated by your extremely finite knowledge and AI Progress resources. So, there are resources that you spend and earn that are finite. It's just that because of the nature of the game, having limited resources overall would completely screw you over and have a massive influence on how the game is played at a fundamental level. AIP would likely need a complete overhaul.
The Crystal isn't limited. It's still unlimited just like the "main" resource, but you have to find planets to mine it from.
In fact, the planets you'll be taking with those features you listed (tech, map control, factories, etc.) will most likely already have Metal and "Crystal" on them. My point is that unless you want one of your resources to stall, you'll have to tailor your Technology unlocks to whatever your resource situation is.
This isn't that difficult or strenuous on the player. If you have a lot of metal, then use your knowledge to unlock units which cost a lot of metal. If you have too much Crystal, then start unlocking those units.
If we just make the resources interchangeable as they are now, then we're just stuck in the same position.
It used to be that choosing units based on your Metal or Crystal situation was actually important, then people whined about the kind of things you are now. Instead of asking players to adapt to the game or the scenario, they wanted the game to adapt to them. Well that's fine, except it takes away a lot of the strategy. Because the resources are interchangeable, I can go the same strategy every single game, even if it is metal or crystal heavy, regardless of my economic situation. So what you inevitably lead to is a situation where the players can just do the same unlocks and builds over and over without any drawbacks.
I don't think this is the way AI War was intended to be played. This is made clear by the fact that so many elements of the game are random like ARS unlocks, fabs. and resource deposits all over the galaxy.
If you went the same strategy in any other popular RTS every game, you would lose. Yet I can pick the same bonus ship, and unlock the same things, every game, even on difficulty 9, and win every time; and nothing is stopping me from doing that. You tell me, is this the way AI War is meant to be played?
The difference is that Starcraft 2 is a zero sum game. Units don't pop out of thin air. And both players are fighting for those resources.
Since the AI doesn't produce units, and no players are competing for resources, any comparison for economy is diluted at best.
Actually the players usually never "fight" for one another's resources, the game is typically over long before that. What they will do is try to prevent another player from "expanding", or in other words deny him from increasing his own resources in some way.
That DOES exist in AI War. The AI's resource is AIP, which the player can reduce with Data Centers, Super Terminals, or by being very careful in what planets he/she takes. The AI can't take away your resources, but it can destroy your army or destroy your planets to prevent you from holding on to them.
So it's not as different as you think.
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Finally, Keith could add a new Knowledge unlock that would transfer one resource type to another, but it should cost around 5K knowledge, and should have a pretty crappy conversion rate.
In other words, the player is ecnouraged to adapt to their own economic situation.