a really unique and fun metroidvania that i've fallen in love with in recent times is the extremely underappreciated
Insanely Twisted Shadow Planet. it feels like the kind of game that would be an "artist game," something with a beautiful art style but mediocre gameplay and bad ideas, but no, the gameplay is excellent and has some really creative ideas. you play as a UFO, trying to fight back against an infectious growth that's taken over your planet. as a UFO, you have several utilities at your disposal, a grabby hand, a scanner, a blaster, a buzzsaw, etc., which are all useful in combat, exploration and navigation. it's such a unique take on the genre, and it's earned its spot as one of my favorite games of all time. funnily enough, i think the first time i heard about this game was when it did a promotion with Del Taco of all places, and it stuck in my brain for years after the fact. i think i also saw Ross and Barry play it on Steam Train, though i don't remember if they finished it...
for a more traditional metroidvania, i'm quite fond of Axiom Verge. i played it a ton on my PSVita when i first got it, and it's such a killer game. it's definitely more metroid than castlevania, but i've always liked metroid more anyways. you play as Trace, a scientist from earth who's been transported to an alien planet called Sudra. you have one simple goal: make it back home, and maybe get some research notes down in the process. i really love the visual style, it does a phenomenal job with the limited palette and is what all "8-bit" games should strive to look like. i remember the weapons being a ton of fun to try out as well, you get a ton of different guns with unique properties that all have their use cases. i dont think i ever beat it, but i got to the final boss, so i saw most of the game. it's really good, from what i remember.