Just finished the game. Unlike something like Breath of the Wild, this doesn't reinvent the formula. It's a pretty standard follow up from what the series had done in Samus Returns. That being said, it's probably the best of the 2D Metroids, and considering how good they are, that's high praise.
The controls build on Samus Returns and make Samus finally feel like an agile killing machine as she should. The boost and especially the slide are godsends that really should have been added to the series earlier. The level design is great at subtly nudging you in the right direction without actually telling you where to go like in Fusion. Boss battles are the best in the series, with a nice blend of giant room sized monsters and smaller enemies that match Samus' agility. Most of the bosses took me numerous tries, but I never felt like they were unfair and never felt frustrated.
The complaints I have about the game are mostly nitpicks. I would have preferred a few new powerups. There are only a couple of new offensive abilities, and neither are especially useful, except for speciffic puzzles. Also, while it's kind of fun to explore every nook and cranny for power ups, the lack of variety in those hurts. Most of the time you get a missile upgrade, and even though I wasn't that thorough (I think I got 60something percent of the items) I never came close to depleting my missiles. So, once I was comfortable with my health, I didn't feel much desire to explore.
The Emmi are kind of meh. I had the same issue as I did with the family stalking you in RE7. Once you've seen all there tricks, and realize that dying won't actually set you back too much, they become a nuisance. Would have been cool if the designs of the Emmi changed significantly, or their attacks. It's a neat idea that doesn't fully work.
All that being this is easily my GOTY so far. Dunno what it is about Metroid but the series just sucks me in like few others. Most of the time these days I'll play games in 30 minutes to an hour sessions over several weeks. This one I played pretty much every free moment I had till I beat it. There's just something about Samus.