Feedback N°1: There is no grass at the bottom of lakes.
Feedback N°2: The number one thing that is ugly in most of digital terrains is how elements connect together. That is how a tree connects with the ground or, in your screenshot, how a body of water connects with the ground around it, etc. So a nice touch to your engine would be an automated river bank generator of some sort. Try to base your work on some photo material or better: go check some lakes and rivers yourself! Even if you fail to implement it properly, your professors might find the method commendable.
As for me, I am still doing weekly para-games on
Retro Sabotage.