I very much admire the dedication to stick with coding and designing SV, but I also understand at some level how it works. But creating the art and music may as well be wizardry. Eric being able to do that also is awe-inspiring.
Toby Fox (Undertale) and Dōkutsu Monogatari (Cave Story) are a few other notable solo devs
Doukutsu Monogatari is just Japanese for Cave Story. The dev is called Daisuke Amaya (Wikipedia informs me).