Nice game, could be very fun and has potential but I don't like the "No energy=very slow move and no fly", I always get stuck inside caves with no energy like 5-10 minutes of gameplay. And believe me, I like roguelikes and games with permadeath adn difficulty but this is not that, you don't die, you just get stuck inside a cave, and can move and go deeper and deeper but can't return home and also this game is sooo bad balanced. Example: I find 5 coal and bring it to my base and get 100 energy, cool, isn't it? Well, no, because I used 5000 energy just to get the coal. That makes absolutely no sense. And to add to all that, found bugs:
1.- At the begining I thought it was a bug but I now think it is part of the game, when you have no energy you cant almost move and cannot fly so you can not go down to the caves cause you would get stuck forever and starve to death or smthng
2.- First time I realised I need coal to get energy I found some, I drill it and nothing appeared in my inventory (three slots available), then I upgraded the drill and won't work, coal not mineable. So I restarted the game and lost my progress
Just change the balance of the game, I have some ideas, one, you could make the energy not to be lost every second even if you are not moving, you could make the movement havea energy cost (and also that energy cos not to be 50 per second cause that would make the game unplayable as I said before, 5 coal found using 5000 energy) or you could transform energy just into another crafting material, you just spend it in things, also you could make the drill robot itself have a "Battery" part you could recharge in the Battery building and then go down, also when you respawn, you do it with full drill robot battery, you would just have to be careful of not losing all your energy but you must not be afraid of losing all your energy
Whatever you do, try to expand gameplay time to more than 10 minutes, I like to spend hours playing games, even if it is a minigame or those "Build things an wait 4 days for it to be built"
A game that could be very addictive and fun if it wasn't for the annoying bugs and balance. Like I would REALLY love to have more than one base and have the last tier buildings and so but I can't if I use 5000 energy to get only 100