I played this one a few years back but never finished it til now.
It's one of the more unique entries for sure. I haven't played much of the remakes (only the first hour or so of AM2R), but I think this game's hasn't aged as much as some may claim.

The controls are very tight and the level design is still very good. There may not be any color, but each area packs an impressively dense atmosphere for a Game Boy title. The vast open areas contribute to making each setting feel more like a long-lost civilization, even if they get kinda annoying when you gotta move a lot to explore it all.

The metroid fights get repetitive, but at least they keep you on your toes at all times. I had already been spoiled some encounters, but there were still more than a few that surprised me. I think the small field of view contributes to the feeling of anxiety.

Over all, it's short and its relative linearity makes it feel quite focused, tho I understand if that's boring to some. In all honesty, I think Metroid II holds up quite better than the original Metroid.