Every game needs ground before it needs anything else, so that's where I started. The first version of Zentura was a procedural world made of blocks that streams in around you as you walk, with forests on top.
Getting there was mostly a fight with loading times. The first builds took ages to get you into a world. Moving the chunk work onto background threads, sharing data between them and caching heights got a new world loading in about 9 seconds. It's not exciting to look at, but everything after this depends on it.
I also added saved worlds with autosave, a basic inventory on a tablet your character holds, and an animation viewer so I could actually see what the character was doing.
No gameplay yet. Just a place to walk around.