If I am not mistaken, once you can enable turbo mode you can reap obscene amounts of experience by just leaving the game idle on Critical training. Experience seems to be related to time spent in training times level and not its results. I wonder if this is intentional.
It's a short and fun game, which can be finished in half an hour. Any attempts to make it more challenging, for example by upping the cost of upgrades, would raise the tedium of drilling to unbearable levels. Though I wish the robot was faster in the beginning.