The environments are well done in their own right. While the Game Boy original largely had flat black backgrounds, here every area has unique backgrounds to each area and areas within those areas. I'd frequently glance at the background and see machinery moving or collapsing, alien lifeforms resting or moving along the walls, or storm cells on the not-so-friendly surface of the planet.
This is complemented by a soundtrack which borrows elements from a few different Metroid games, namely a couple tunes heavily inspired by Super Metroid's soundtrack, and even borrows a few sound effects from it. The songs range from haunting to energizing and almost always work well with each action and environment, save for maybe the first part of the credits roll. When the theme for the surface of SR388 started up, I was locked in.
Enemy variety is a little lacking in some parts, with a couple particular ones getting palette-swapped and given slightly different abilities. I'm talking about common enemies, not the various Metroid mutations you hunt throughout the game. That said, it didn't bother me in the slightest as Metroid II had the same issue. Not excusing it, just saying it's a common thread.
Boss encounters are challenging at first, but still generally simple to figure out what to do to beat them. That's only half of it, however, as most fights in this game require equal parts strategy and proper execution of said strategy. The Queen Metroid and the Diggernaut in particular have a heavy emphasis on execution.
I've completed the game once (in about 10 hours) and am going back to 100% the game, since each area has several sections with items you can't reach without power ups from the later stages. This is made less of a chore by the teleportation stations scattered around the map, which can send Samus from one end of an area to another or to another area entirely. I, for one, welcome this as a way to take the tedium out of backtracking for completion's sake.
There's another reason I'm doing this, which is the Chozo Memories gallery, somewhat similar to what Prime offered but in a different format. Tied to item completion, it shows images of the Chozo civilization before it completely fell to shit, which are divided into four parts, each unlocking separately based on your progress. I'm a sucker for lore stuff like this so I'm anxious to find out for myself what all of them are. It's a nice incentive to not just drop the game after getting through it once.
Metroid: Samus Returns is exactly what I hoped it would be. It's a great take on a classic formula with some new tidbits thrown in that make it a unique experience from its source material. It sucks Another Metroid 2 Remake got taken down, but it's nice to see that it wasn't in vain considering how well the official game turned out. Despite my concerns, leading up to its release I was hoping I'd be able to say what I'm about to say, and now I can finally say it.
Good job, Mercury Steam.