Pretty decent. The rooms are solid, both from platforming and the tiling, palettes, and use of fx. The music and sprites are all customized, and the menu/ending are nicely changed to reflect the lack of metroids or exploding planets. There aren't any mechanical changes like respin, but it does have updated map tiles to help with navigation.
There were some frustrating parts; choosing the "wrong" missile door early on, the finnicky precision in the first stretch, and a grapple trick. Though, that last one is more personal preference/comfort than being a problem. The final fights / boss are neat, though I died several times and found running back to be a bit of a slog.