I guess this really is the first Metroidvania since it did come out a few months after the other two. Probably not directly inspired, but it sure feels like it. You also seem some Super Mario Bros flavors added here. (The boss fights come close to straight up plagiarizing Bowser's movement from SMB). Overall it's really a solid action platformer with some really nice attention to detail in some animations and level design. My biggest gripes are that there are too many destructible blocks which forces you to run around the entire game shooting at everything and the music minigame is basically Avalanche and I hate Avalanche.