Spoiler
I finished it Saturday and 100%'d it yesterday. I don't have any interest in Hard Mode at the moment; in fact my reaction to seeing "Hard Mode unlocked" was a swift "no." Game was great but at the same time it felt like it needed to dial back the damage a bit, also I feel like the game should have at the least some accessibility options because I feel like the difficulty would just be a turnoff for a number of new fans. I mean, those looking for a challenge will find the game rewarding, and that's good, but less-experienced players might not be so interested in continuing after a point.
But that tangent aside, I personally highly enjoyed the game overall. It didn't improve too much in the music category admittedly, but the gameplay was so incredibly solid and the level design was a step up from Samus Returns. E.M.M.I.s are the best part of the game by far and make great tension, as well as great satisfaction. The overall length felt just right and just in general it was fun to play. The story was surprisingly good too.
Honestly, I do hope this partnership with MercurySteam continues with new games. It's an amusing "redemption story" since I did not like their takes on Castlevania at all, but with Metroid something seemed to just work. Again, it's quite a refinement on what they created in Samus Returns, and it's a formula that could get even better as well. God, it's so good having Metroid back, I just hope this holds.
Now my sights are turned towards Prime 4. As much as I was amazed that Dread was actually happening, as glad as I am to have a new 2D Metroid game, as good as this game is and as much as I enjoyed it... at heart, my true love is the Prime series.