Thanks for the feedback! I still have lots of work to do when it comes to balancing.
I am also looking into some form of comeback mechanic to solve the problem of having to restart after losing, any ideas are highly appreciated!
Maybe you could add an additional resource that the player gets for killing enemies. This resource is not lost when losing and can only be spent between runs. In that way it would be possible to grind a few runs and then start with a stronger army. Also the player should have always at least 1 marine ...