this game is very reminiscent of Metroid II, which was one of my favorites for the old game boy system
i've just beat this game and the included map was handy enough for me to find my way around. unlike metroid II, the tiles in each area were different enough to distinguish on their own.
the game does have some quirks, most notably a lower framerate than usual and no knockback from enemies. this doesn't take away from gameplay much, but it does end up being a little less challenging than i'd prefer when everything runs in slow motion and you can tank damage during boss fights with no consequence if you fire fast enough
overall it was pretty enjoyable, with pleasant graphics and a good flow in backtracking with the level design