I think Kid Icarus occupies a similar place in Nintendo's library as Vampire Killer did for Castlevania. It's more obscure than Metroid, but both games were designed with the same engine. While Metroid was an attempt at a more open-ended design, Kid Icarus is more linear. On top of that, I think Metroid focuses slightly more on enemy designs to flush out its stages while Kid Icarus is a more difficult platformer. All in all I prefer Metroid to Kid Icarus, but despite some tedium, you can see that just as much effort went into this game.