That is some wonderful pineapple texturing

Colors are part of it. Irregular colors get confused with shading. Weird shapes a lot of rocks naturally take just look bad in pixel art. I also don't know part of my problem with good rocks. I just know I always have to redo my rocks.

It takes a load of practice to get right. Especially for rocks in pixel art.

You will want to focus more on shapes than lines. Your characters and the vehicle are more shape focused and turned out great. The rocks behind them have great shapes on the large scale, but the overuse of horizontal lines muddles this.

The way viewports scale pixel art makes that very tough. I keep the interface out of the viewport, but for split screen that would require a lot of coordination. The easiest option is to have the labels be pixel art instead of text.