The best that Metroidvania as a genre has to offer. Unparalleled freedom of exploration, insane built-in movement tech that allows you to snap the game in half and complete it in any conceivable order, varied and challenging boss fights that are a joy to play and make you wonder how did one man ever come up with so many dank bullet hell patterns.
Nothing will ever compete until TEVI comes out (which is made by the same guy, isn't that cool)