I adore Metroidvanias. Hollow Knight is constantly in my top 3, I loved Blasphemous, the Ori series, even Metroid itself. I know a lot of people say this is a loving homage to the Castlevania series, maybe I'm just not a fan of Castlevania (never played one). Let me start with some things that I liked and I'll go from there
PROS
+This game is visually stunning. I love the art style and the 3D models in a 2D world really does something for me.
+The sheer variety of weapons is something to love, especially as each has their own special moves associated with it
+The shard system was super cool, allowing you 2 active skills, a passive, a "hold" skill that requires you to hold a button while using it, and a familiar. The combinations here are endless
+Each area feels super unique and well crafted. Just like most other metroidvanias I've played, each has areas that are inaccessible until you acquire a certain ability.
CONS
These are big ones. I have a few small nitpicks, but I want to get my main frustrations out of the way
-The only way to "beat" this game and watch the credits roll is to damn near 100% the game. I found the "final boss" on complete accident and killed him first go. What am I met with? A short cutscene and a game over screen. So I looked up a guide which leads me to my second gripe.
-The way to watch the credits roll is convoluted as all get out. I'll try to leave as many spoilers out as I can, but read at your own risk. First you have to figure out how to get underwater. Good news is there's a shard that lets you sink to the bottom of water whenever you want! Bad news is the path to get there is underwater. You see the issue here? You have to kill a specific enemy to get a chance at them dropping a specific shard, none of which is told to you at any point. Unless your playstyle was "get all shards as soon as they're available" from the very beginning, you're going to need to look this up. Smooth sailing for a bit, then you need to cross a spike hallway. You need a very specific set of armor located on the dead opposite side of the map. And then... and then... and then... go find ANOTHER MOON... and then... I love doing 100% runs of games, just not my first playthrough. And this game REQURES it if you want to see credits.
-Again, just my opinion, but the combat is not good. You have one attack, and weapon-dependent specials that require special inputs. Your dodge is a backstep that honestly not as good as just running the other way. Plus is BACKWARDS. You have to face the attack and dodge to move away from the attack. Very counterintuitive.
-The bosses are nightmares. Each and every one is fast, unpredictable, and hits like a truck. Not to mention that, most of the time, they're hard to hit. The very last true boss almost made me quit the game altogether, especially considering it came right after a different difficult boss.
And that's that. I think a lot of it is nostalgia, which I don't have for this franchise. Who am I to argue with 26,000 reviews on Steam with a 94% positive, though? If you're on the fence after reading this, read a few from people who enjoyed it. I personally could not wait for it to be over after a certain point, so I may not be the most reliable source.