Many aspects of it completely ignored in the tutorial called "Dig" and features that you can only find out by checking settings hotkeys doesn't feel right. I get it that it's a complex mechanic that won't fit in 1 tutorial page but leaving player completely clueless isn't right.
How is there no hotkey for "Keep" feature. I actually wanted to find that one after finishing the game thinking to myself - I can't believe that one doesn't exist. It seems like a very useful option to collect resources without drawing big shapes or hovering cursor in place for multiple seconds.
Instead I found two more features for digging sand/nonsand and digging ship shape. Both of which work in unintuitive way.
- Dig sand selects sand/nonsand by the type of first block that gets marked. In dynamic game with sand falling from ceiling every time you expand your cave you probably can miss the those 2 small sand blocks that won't let you place your ship and you will remove your floor shield instead.
- Digging ship shape doesn't require clicking over the terrain. It instantly marks blocks for removal the moment you press Alt. Every other dig operation require holding LMB and you assume this one also will wait before you find good spot and press LMB. I can easily imagine this can cause unwanted walls getting removed quickly.
So without all that yap I suggest:
- adding hotkey for "Keep" digging so we can collect sand/water resources by clicking once in the lowest part of them.
- split Dig sand and Dig nonsand into 2 hotkeys so it won't select opposite of what you want by the type of block you hover first.
- require LMB being pressed to dig ship shape.