Very solid Metroidvania and an impressive GBA launch title, Circle of the Moon was very fun to revisit and finally beat. The DSS system is really cool to mess around with and adds tons of variety to both combat and exploration. The exploration, while way less complicated than most Metroidvania games, was super fun and most areas were fun to explore. Being a GBA game it's relatively short and doesn't overstay its welcome being a nice in and out experience.
My main gripes with this game were three things
1. The GBAs screen crunch issue that was present in many of the early library. While it wasn't as bad as some other games from the era it was still frustrating to get blindsided by some projectile offscreen.
2. The low drop rate of DSS cards was kinda sad as the DSS system is one of the most fun parts about the game. By the end of the game with the entire castle minus arena explored I only had 5 cards without grinding. This is somewhat alleviated by the glitch that lets you select any card but its not perfect as that just completely breaks the game. It just needed either a slight drop rate boost or a way to just find them on the map.
3. The massive difficulty spike around half way through the game. I remember when I first played Circle of the Moon as a kid I could never get past Adrameleck and the game only gets harder from there. It wouldn't be so bad if the DSS cards were more easily obtainable but again the low drop rate (or my bad luck) made some sections an absolute pain in the ass.
That said some of this frustration is admittedly (and accidentally) self inflicted as right after fighting Adrameleck I went straight to Underground Waterway which, without the purifier, is Super Adolf Blight Town Deluxe. I simply thought there was no other way to go and didn't realize I could slide until right after I beat Hugh. It's cool that you can sequence break and it's probably my fault for not realizing such an obvious button combo but holy fuck I wish that the game gave a little more direction about that to have saved me the trouble.
Overall Circle of the Moon is a really solid short romp. Not as good as other Metroidvanias like Symphony of the Night or something but it's fun little ride if you're a fan of the genre.

Completed at slightly above 90% completion rate at around 7½ hours and felt alright with those numbers. Castlevania: Circle of the Moon marks a successful proof of concept to continue the Symphony of the Night direction of incremental upgrades allowing greater map exploration. Circle of the Moon comes equipped with interesting new items and mechanics, emphasizing the RPG-styled progression from before with more expansive options to customize the game experience. The customization is solely thanks to the DSS or Duel Set-up System, where players combine cards dropped by enemies to create different effects that assist the player. On-the-fly experimentation can supply a longer whip, fireballs surrounding and protecting the player, turning the whip into a giant hammer, and much more. Though the card system adds a lot to the experience, relying solely on random drops for these cards means grinding the same enemies repeatedly, hoping you'll get a card drop so you can move on. The game is generous in telling you if a enemy has a card to drop and if you have it, so this could be far more stressful than how its already implimented.

Speaking of killing enemies repeatedly, the map design does leave something to be desired in how the player backtracks old areas. It's the literal name of the game, which is to explore new places and defeat bosses to get new abilities so you can go back and find new stuff. Running through the same areas repeatedly with little to break how you navigate said areas gets old after a while. Not until you can finally launch yourself into the air towards the end of the game does any movement upgrade feel substaintial, and is too little too late by then. No amount of spawning newer, more challenging enemies in old areas can make the leveling and exploration feel as impactful as it should, either.

All these negatives aside, Circle of the Moon is still a great game. For a GBA launch title, most of my expectations are met for a great action title. Exploration is plentiful and there are secrets plenty. If you're a sucker for severe punishment, a gauntlet of obnoxious, incremental arena battles are available to grind. Being a game released before publishers could charge for more modes and cheats, Circle of the Moon has ceaseless unlockables and modes to toy away at to maximize your time with it genuinely. Even if the later entries dwarf the first GBA Castlevania, this is leagues better than the trash I was playing as a child. I would've traded nearly any other game I had for something as replayable and complex as this.

Given I haven't quite finished it at the time of writing (game hard), I don't quite get the hate surrounding this one. It's definitely clunky, probably quite a bit so compared to newer entries, but for me, Circle of the Moon is a great fusion between the things I like about classic Castlevania and presumably, the things I will like about "metroidvania Castlevania", this being my foray into that style of the series.

First off, I really fw this game's difficulty, tight as it is. While it's possible to grind for levels and recovery items, my goofy ass is stubborn and impatient, and I tend to run past encounters with spongy enemies. Often this leaves me high and dry for the boss fights, but I honestly can't say I don't get a sick kick out of that. Finally beating a tough boss after hours in the salt mines is a favorite feeling of mine.

Good music is another thing Circle of the Moon possesses in no short supply. Castlevania is full of bops in general, and this entry's no exception. Even the driest of exploration turns to mad vibes when met with the right tunes. Unfortunately, I think that exploration is where Circle of the Moon (and in fairness, a lot of other metroidvanias) can fall a bit short.

While this game offers solid level design and a lot of cool, useful things to discover, obtuse progression is a staple of its genre and not one it's exempt from. Often there is only one way or a few specific ways to go, and while this is relatively common in metroidvanias, it is no less egregious here. Circle of the Moon also occasionally lets you sequence break to an extent. This is certainly not a negative in of itself, but due to the game's sharp difficulty, it's totally possible to scrape yourself into a certain late game area like fifteen levels early, only to be met with an absolute brick wall of a boss fight. To be honest, I find this kind of thing sort of commendable, only in my case I did this on TWO separate occasions thinking it was the only way to go, having to painstakingly backtrack the entire length of it both times (AND IT'S A POISON SWAMP). I'm probably just stupid, but I'm admittedly still butthurt lol.

Overall, I've found Circle of the Moon to be an incredible time, just one I can't really recommend to everyone considering its fair share of retro game bullshit; sluggish movement, obtuse progression, and comically low item drop rates. With that being said, I think this version might have save states, so it's probably worth a shot if you're normal and don't mind using those. Formidable but fair vibes for sure.