- Single player, wich is awesome for the first several times, but later - became tediouse, unless you are chasing some wierd goals like huge for the sake of huge, or building x86 because you can.
- Cooperative multiplayer, highly cooperative, several people building the same factory. Amazing because of socialisation, cooperation and fun.
In competiteve play you and your opponent(s) are building separate factories on the same map to decide who is the fastest, the most efficient and ultimatelly the best engineer. It adds pressure no amount of biters could provide. And noone messes with your perfect base like in cooperative games, because you have your own base.
And all the required tools already exist in the game.
All we need is checkbox "each player start in his own faction" some settings for damage/friendly fire/disassembly control, and maybe adjust map generation a bit to generate separate starting areas.
It very strange the game have all the tools to make significant part of the community happier, but it lacks very basic lobby interface to use them.