What makes different grades/types of matcha tea distinct from one another?

Organic farming of matcha requires much more effort and hence demands a higher price. All organic matcha tastes grassy. But high-quality organic matcha tastes smoothly and delicately grassy, and is very enjoyable. Non-organic conventional matcha varies much more widely because the plant is typically fed with synthetic chemical fertilizers to influence its taste. I recommend you do a side-by-side comparison of organic and non-organic matcha and see what you prefer!
In general, matcha from Japan has higher quality than matcha from China. Even that matcha originated in China, Chinese farmers stopped the matcha way for a few centuries until a recent comeback in interest.
Matcha grades and products do vary distinctly from one another. The main factors are harvest, origin, plant and leaf quality, organic or not, processing technique. All other things equal, first harvest matcha tastes smoother and looks greener than later harvest. Always ask the matcha brand which harvest and month its grade is from.