Fantastic way to learn the basics =D would also be great to implement down/uploading savefiles manually. When this game gets biggerover time, I don't think my cache will store data that long. But all in all:
5/5
would be great to add some kind of checkpoints with passwords.
This way you could continue even if there are no savefiles.
Time-Taking, but interesting ;D
i think you should totally avoid building sentinel guns, they may slow down your computer very much when shooting. just build a floor of some mines and lifters. some turrets and a trap of saws in the middle will help for fast scoring (~ 5-10k per second)
Thanks for the feedback, added a +5000 button