It's rather abstract... so if I understand right, you let the world evolve while the player is playing it? Not like the usual world generator where the world is generated once at the start, but after that it's only the player changing the world.
It might be interesting to see the ecosystem behave in a reaction to what the player does. Perhaps the player is not seeing the tier 1 resource you call "energy", but his actions could alter it?
Also, do you have a goal or story in mind? There is an ecosystem, but that alone doesn't sound like a "game".
Special poison tipped bullets - messes with the enemies' head so he goes berzerk and takes nearby allies down with him in his last seconds before dying slowly. Great when you face a crowd of enemies, but only have 1 bullet, just make sure you don't shoot him in the head.
A little portal addon - you place the portal in the wall where you know the enemy will pass, and move yourself to a safe place where you see when they are near your portal, then shoot; instead of the bullet exiting your gun, it will exit the portal. After you shot they detect and destroy your portal instantly and probably know your position too, so make sure its a hit. Great to use with a RPG launcher.