I like how at a few points new technologies let you totally redesign your board. I ended up with mine mostly empty and even spent a few rounds just tweaking aesthetics. The final board size upgrade seems largely unnecessary unless there are going to be even bigger buildings in the future.
Overall I wish there were more building interactions. Solar panels get better when they touch at least one other solar panel, and farms grow more when they touch a water source. I think you could break the water synergy down into tech unlocks for each water source or farm type, and that could make the tree a little smoother, especially towards the late game when you can unlock a 400 science node every turn or two, with only two observatories. Having synergies for windmills could make them worth building, I built four. You could even have synergies that reduce costs instead of increase products, like putting windmills next to oxygen buildings reduces power consumption, or something.
For a hard mode, you could have building conflicts, like putting a mine next to a water source is bad somehow or contiguous water sources are less effective “because the water table is getting depleted” or something.
I did have a performance issue just before I unlocked the geothermal power, where I had so many solar blocks that picking up, and more so placing every building would take upwards of a second, and if I tried to pick up another building too fast, it would grab the last building again even though the cursor was far away. This went away when I was able to reduce my building count.