Mechanically superior to the original Metroid II, but lacking in a lot of the heart. The game blocks your path anytime you try to get clever with bomb jumping, and seems like it doesn't want you to think outside the box in exploration. It's a remake of a linear game, so having crazy sequence breaks isn't expected, but it feels like the game overly dictates where you go and in what order. New roadblocks are added for new and old items alike to basically require you to get all your abilities, whereas Metroid II left a lot optional, instead acting mostly as helpful boosts to your power rather than requirements. Even the freedom to choose what beam you want to use (even if the options weren't conveyed very well in the original) is removed in favor of beam stacking.
But what really disappoints me is the change in atmosphere. This 3DS game from 2017 has worse atmosphere than a 1991 Game Boy game. The original was creepy, with weird noises echoing in the background that made you wonder, “What is that? ...Are the Metroids making those sounds?” And any time you did run into a Metroid, the little jingle was almost like a jumpscare, and the following fight, thanks to the chaotic music, felt like a scramble against a beast that's stronger than you (especially against later forms). For as much as it could be on a monochrome screen in in 1991, Metroid II was a horror game. I remember the tension of creeping around with low health looking for a save point, hoping not to find any Metroids along the way. I remember the Metroid Hive, and how the music became unsettlingly detuned after the sudden Metroid spike. And I remember the final moment of calmness as you walked back to your ship with the last Metroid, the prospect of a galaxy at peace finally possible.
But Samus Returns throws most of that out. Lots of the music is retained, though there's also some tracks from other games thrown in there that, while great songs, don't achieve the same atmosphere. The planet feels a lot more vibrant and alive, featuring rich greenery and pools of water in later areas. But isn't that a bit odd, considering that the Metroids are apparently ravaging the planet's ecosystems? Metroid encounters are missing tension, as your indicator alerts you when one is near, and you can simply respawn right before the fight if you die. It feels like you're hunting them down, seeking them out, which I guess is a bit closer to the game's plot, but carries a very different mood than the original. Fighting the Metroids in Metroid II wasn't particularly fun. It wasn't really something you wanted to do, and I might just be reading into limitations of the time a bit much here, but I like to think that that's sort of the point. It's a game about committing genocide. That ending is a breath of fresh air, a moment of peace where you spare a life because it's the right thing to do, and after an entire game of it, it's time for the killing to be over. But Samus Returns makes genocide fun. The fights are proper fights now, complete with the doors locking behind you until you defeat each Metroid. As Samus does sick flips while blasting missiles, you might sit there thinking something like, “Take that, Metroid scum!” Some of the poeticism is lost. The Metroid Hive lacks the amazing build-up of Metroid II, the scenery is less ominous, and as mentioned by many others, the abundance of normal enemies and the surprise final fight against Ridley ruins the entire aim of the original's ending. While I like the idea of some moment to create a stronger bond between you and the baby Metroid, it just doesn't fit into Metroid II.
Samus Returns is just too focused on being an action game to realize some of the subtleties of the original. But dang, is it a good action game. Boss fights are a blast and its difficultly feels fair, since enemy attacks are all able to be dodged with enough skill. The 360 degree aim and melee counter feel great, though it bugs me that the latter means every enemy now lunges at you the second it sees you (no way every single animal on the planet would be that aggressive!). But Samus's arsenal is generally very well used, and both the new abilities and quality of life improvements are greatly appreciated. Plus, each area actually looks unique now, instead of all being same-y ruins (though I do miss a lot of the later areas of Metroid II)!
All in all, Samus Returns frustratingly misses most of what made Metroid II special, but the core action gameplay it has is fun enough for the game to still be a good one. Just if you've played Metroid II, you'll end up liking Samus Returns for very different reasons.