Hollow Knight: beat the game, 100% completion, in just under 40 hours.
Here is the release trailer for the game. Go ahead and watch it. Think of the best-case scenario for the game, based on the trailer. That's pretty much the game you get.
It makes me immeasurably happy that some 13-year-old kid is gonna play this and it's going to be their first metroidvania. It is an orthodox, highly polished example of the genre, and whereas I've played a lot of metroidvania type games recently, and they have been good to great in their own ways, this is by far the best at BEING one. You will explore zones. You will retrace your steps. You will get powerups that allow you to poke and prod at the corners of the map. You will do things in an order of your own choosing. If metroidvanias are your bag, play this game, period.
Other thoughts:
The game is very large for a metroidvania. I ran out of leads looking for more stuff to do (other than fight the final boss) only at about hour 35. That last 5 hours represents sheer stubbornness in not consulting an FAQ for the last few things I was missing.
You get a large number of potential powerups, which you have a maximum capacity to equip at a time. For the tougher bosses you'll find yourself experimenting with different loadouts to see what works. Boss fights all allow for flexibility in how you approach them.
Holy shit there are a lot of enemy types. 144 to be exact, including bosses, and none are pallate-swaps. Production values in this game are through the roof. Really.
Although the plot does not have a ton of depth, the game has a theme, and executes it beautifully. By which I mean both that it is elegantly handled, and that the main plot stuff is fucking gorgeous. The final boss sequence is spectacular.
The game does a Dark Souls-y thing where when you die you lose all your carried money and 1/3 of your magic capacity and need to go to where you died to fight your soul and get it back. Ok mechanic for a while, but you run out of stuff to buy way too early for it to work very well in the long run. Thematically, however, it works great.
For anyone who plays: if you quit to title and reload, you will end up back at your last save point. Do not be bashful about using this to travel.
On that note, the game is huge, and there are a few spots that are just too far from fast-travel points. No big deal for 90% of the game, but when you're hunting down powerups it can be a bit much.
The game's save points are all benches and I am convinced it is an Ico reference. The game has a bunch of references, and can be pretty blatant about them.
Nothing in the bestiary is permanently missable. Thank god. The game actually goes out of its way to ensure that this is the case.
Your health pool is pretty low, you start with 5 and take 1 or 2 dapage per attack, but you can heal with magic off the bat by focusing in place for a couple seconds. Additionally, you replenish magic by attacking and killing enemies. This is balanced very well in practice, both for exploring and for boss fights, which have been clearly designed to make you have to be very careful about when to heal.
I guess saying the game is the best-case scenario implies it but anyway: movement is very fluid, and the wall-jumping and other midair platforming elements are very adaptable and feel great to use. Which is good because there is a brutal platforming segment late in the game.
The music! Is good. Occasionally great. City of Tears is a standout. Final boss music, too.