Played through a bit of Metroid (2): Samus Returns; I've got the Beam Burst and Grapple Beam, only really just starting to get into Area 3. It's... not a bad game by any means, but... I get the feeling it could've been loads better had they simply stuck with the control scheme used in Metroid 4: Fusion.
What I'm talking about is my biggest complaint about the game: They wanted so badly to make it 3D, when it absolutely should not have been. Metroid II: The Return of Samus was what it was precisely because it was 2D; could you imagine all the havoc having that version of the Spider Ball in 3D would cause?
Nintendo at least recognized that much, but even so, they really wanted to make this as 3D as they could make it. Hence, you can aim your gun in 360 degrees around you --- buuuut, you need to halt all forward momentum to do so. And, as a result of this ability, enemies are literally everywhere.
In order to deal with this shortcoming, they came up with the parry attack: Basically, when an enemy charges at you, often from a difficult angle, hitting the X button at just the right time allows you to parry, which knocks them off-balance and gives you an opening. You are then auto-aimed to the enemy you just knocked out, and usually can get a one-hit kill with anything but the ice beam.
They really, REALLY wanted you to use and master this attack strategy, because in order to defeat some of the Metroids, it's basically necessary. So, in addition to making the parry attack a one-hit kill, they made pretty much all enemies you can use the attack on incredibly difficult to kill otherwise. As the game progresses, you start to encounter enemies with armor that are literally impossible to kill without this attack.
This in and of itself isn't really too bad; it's just another weapon in Samus' arsenal. You can use it when you need to, right? It's just like the ice beam, or missiles, or bombs. Except, those of you who know the Metroid games might know: Very rarely are you on one screen with only one enemy, unless you're fighting a boss (against which this doesn't work anyway). If two enemies charge you at the same time, you can parry both of them, assuming they would both be in-range; however, you can only auto-aim on one. The one-hit kill only works for your first shot. The moment you fire a second time, you're back to the original schema. Now, with armored enemies, they at least stay knocked out so you can wail on them for like five seconds of nearly-continuous attack before they die, but that's still an inconvenience for a weapon that's supposed to deal with this exact issue they introduced to make you use this attack.
Your one-hit also goes away if you get hit in the interim. So, say two enemies are charging at you at different times, a very frequent occurrence: You hit the first, and then the second knocks out your opening. Or, you miss the first, and your stumbling back disables your parry for the second. There is no winning mode in such a case.
This is especially frustrating when coupled with the control schema of the game. Your free-aim mode is enabled by pressing and holding the left shoulder button, which is mildly reasonable. Your missiles are activated by pressing and holding the right shoulder button, which is a right pain in the ass. Try aiming and charging a shot, too; that gets pretty painful, especially as aiming is done, not by minor rotations of the thumb disc, but by slamming the thumb disc all the way to its limit in the direction you want to aim.
Metroids, with this schema, are frustrating. The first one isn't too bad; it doesn't really throw any curveballs at you, simply charging and letting you parry-attack it (something like ten missiles kills the Alphas). After that, they start throwing in new attacks for them, too. Some Metroids have electricity powers; if they charge you with this, you cannot parry. These types also float around the room and drop little charged bombs that take off like half an energy tank if you get hit while in the Power Suit. Some Metroids have fire powers: They charge at you with fire, which is the same as with electricity, but the bombs they drop engulf the entire platform they strike with fire. That, you know, takes off half an energy tank of health if it hits you early game. Save for the first, all have some sort of power like this.
Don't get me wrong: The Metroids are supposed to be difficult. They're the reason for the game! But when, in the original, an Alpha could be taken out with minor difficulty just because the controls didn't suck and they didn't try like hell to make it 3D, it really highlights the shortcomings of this edition.
That having been said, I'm still having an alright time playing it. It's not bad, just severely flawed in ways that they deliberately chose to do. There are other good things about it; I actually kind of like the Aeion powers. (I just wish they didn't have to use the goddamn A button to activate them; a button that important needs to be jumping or firing, not wasting your time and Aeion just because you slipped up and reverted to a control scheme that didn't suck.) The graphics are lovely, the enemies are gorgeous if perhaps repetitive, and the puzzles are nice. (There was one frustrating puzzle I needed to get help from the internet to solve, because the mechanic necessary to solve it isn't actually introduced at any time at all.)
Is it a must-play game on the 3DS? Eh, probably not. The original, while difficult due to its lack of any sort of mapping system, was otherwise better. But, I do like the things they actually upgraded, so, meh?