Eh. I'm not really a fan of the first Metroid, although my perspective is skewed due to the fact that I played this in the interim between Prime 2 and Prime 3, after all those other, more polished and refined Metroid games. It was too ambitious for its time, that is the only way I would put it, and while I can appreciate this ambition (which would later be realised properly), I cannot appreciate this. I actually prefer it to Metroid II, the lowest point of the franchise in my opinion, because the colour and the zoomed out view is at least slightly helpful for navigation, but it's still not nearly enough. The world design is just not conducive to logical exploration and seriously, the difficulty curve is utterly backwards. At the beginning, it is toeing the line of controller-throwing frustration because Samus is SO nerfed in every way. Then, after surmounting that hill, it gets progressively easier, the Ice Beam being the biggest turning point for me, though I didn't find it particularly fun even after that. I've said before how I despise the bosses, if they can be called that, for being little more than missile cannon fodder. Oh, and one more comparatively minor complaint: Metroid on NES has quite possibly the worst sprite flicker I've ever seen in anything.
That said, I do like the music. I'm sure most will agree it's the best part of the game and the only part that has stood up to the test of time. Great tunes made more impactful by the arrangements in Smash Bros. That's it though. Nothing else is likeable. I haven't played Zero Mission, but I will tell anybody to go play that instead as I'm 100% confident that it blows its inspiration out of the water.