This is a wonderful low poly terrain, the only part I would suggest changing is the terrain underwater, its a bit ‘off’, and you could make the sand slightly darker and the water slightly more visible.
That looks amazing so far, I am guessing you will be adding onto the terrain eventually.
For feedback, I agree with AmusingDev, the water doesn’t really fit with the terrain, you should try making it more lighter and an aqua colour if possible.
If you haven’t already planned or thought about adding to the terrain, here are some ideas:
Add trees, rocks (near shore), small dug up holes, shrubs, sticks, etc.
Detail the small lake too. These include include small parts of dirt, sand, and stone for the grounds surface, living fish, crabs, and starfish for a natural effect, and detailed rocks and reef samples in the water.
Hey, great question!
I actually use a plugin that requires 3 blocks (that is why my terrain is covered in red dots) that creates a triangle and I just build from there. Yes I started building it from air, hope this answered your question!