I can feel it in my own play, my play being faster, build orders being sharper and better decision making in general. There have been multiple times throughout playing StarCraft for me personally where things just started to click and in those moments I begin to feel myself playing better.
That is rewarding to me, to see the practice pay off. I can start a new account and have it be in the master league after a few days solely because I have developed the skills required to do so.
StarCraft doesn’t provide an endless grind to collect the most experience points or get the best equipment/armor/weapons etc. There is always something to do better and finally being able to do those things better after having practiced them for many hours is rewarding in itself. I find it rewarding because of the impossible to reach skill cap that allows us to always be improving. I also play StarCraft because it is naturally rewarding in its gameplay for a few reasons. I play StarCraft because I enjoy it, it provides a fun and challenging experience on a level unparalleled by any other game I have played.