When i heard Mercury Steam was making this game i was worried as i thought their remake of Metroid 2 on 3DS lacked pretty much everything that made the original great while adding new foreign concepts that did not mesh well with the formula.
Now Metroid is my favorite series of all time, two of their games are in my top 5 which are Super Metroid (#1) and Metroid Prime (#4) so some of these things you might see as nitpicks but i am very invested in the series being the best it can be. Overall i really enjoyed the game but we aren't quite there yet in terms of story telling, control, exploration, music, and natural backtracking.
Control - I have mixed feelings about control in this game, they keep the free aiming that locks you in place when they could have easily moved the free aim to the right stick so you can still move while on the ground while accurately aiming. If they gave us options for angle up and angle down like Zero Mission, Super Metroid, and Fusion, i would have used that the entirety of the game instead of this new free aim which gives you iron boots. Although i myself found a solution for most of this by keeping samus in the air as much as possible (where you can free aim while you are rising and falling) it is not a solution for everyone nor a perfect solution in any sense. It does however make the game a lot for fluid and fun which it already is outside of the free aim. They fix the (foreign) Aeion abilites from Samus returns and they now feel more like a natural extension of abilities for Samus that will be missed going forward if they are not included. Instead of an invincibility shield and a gatling gun you get an air/ground dash that can be used three times before depletion and a cloaking ability that slows your movements for the parts where you are avoiding capture. The dash makes Samus more mobile than ever and i hope it never goes away, it is OP in the best sense and can be chained into other movements and techniques.
Exploration/Map Design/Backtracking - Too often i found myself exploring an area to find either a door locked behind me or some kind of mechanism blocking me from going back to collect something or explore something. Like you fall down a pit and a machine rotates so you cannot get up that way again or go around either to get back. You pull blocks with the grapple beam which open new paths while closing other ones. Rocks and debris fall which in some cases can never be removed and you will have to go the long way around. Almost every item you will have to come back for because the game does not loop you around in this area once you have more power like Super Metroid does. For this purpose there is no reason to backtrack until you have the last upgrade and can get everything so you can just do it all in one go. This is not what a metroidvania is or should be. It should feel natural "oh i can now go do that 2 rooms over there" but this is simply not the case for the majority of these upgrades. They give you enough missiles and energy tanks on the beaten path that it is never encouraged or necessary to do so and in some cases impossible to do so by some bs blocking your path so you dont get lost. In the better games in the franchise they will loop you through this area with a treasure trove of assets and then lead you to a path you couldnt previously open that you remembered. That is natural progression and collecting. To get around these one way blocks that deter you frequently morph ball tunnels would have been appreciated to bypass them for people that really wanted to backtrack while keeping the rest on the beaten path.
Story - The story is fine, great even, until the ending where several plot holes open up and things become muddled. I still think it is a good story but would like some clarification because there is for certain at least one plot hole in each way you can interpret the ending.
Music - They use the old themes well and at appropriate times but there is a distinct lack of new music that is anything more than atmospheric. The Water area probably has the best new track but it is very low key and kind of just background noise. Nothing really stands out, i am glad they did not remake the lava track for the lava area for the 18th time but give us something to jam out to, just one. Even the fan remake of AM2R did this, in each metroid you normally have a wealth of good music that sets the tone but it is completely absent in this game except for the classic stuff that is used sparingly (which i appreciate). They need a new composer for the next game they do. The game by all accounts is selling very very well, the best in the franchise even, so they for sure are getting another game.
Combat - Has the best combat of any Metroid game and the best set of bosses which are all evenly balanced with the perfect difficulty
tldr - newer fans will peg this as their favorite, older fans like me are happy with it but it can be improved a lot to be more. The maps are completely disconnected instead of one large world that circles back on itself and this hurts item collection, back tracking, and game flow.