This is just Castlevania 3 without the constant & relentless hostility towards the player that CV3 likes lol.
First of all it looks and sounds staggeringly close to a real 8-bit game. It has some minimal modern visual touches and it runs expectedly smooth compared to NESvanias and their sprite flickering and occasional slowdown, but other than those I think you could go back 40 years in the past and give this game to someone from back then and they wouldn't even notice anything strange.
On top of that it has a "casual" mode where there's infinite continues and no knockbacks for being hit for people that want something more modern and then there's "veteran" mode where the game has the same structure as Classicvanias (lives exist, score can get extra lives, there's life pickups in the stages, enemy knockback is in full force).
I adore the use of colors, the stage designs, the monster and especially boss designs, the music and sound effects, everything about the game's presentation is flawless, and it's topped off with such a good ending screen for those that adore Classicvanias. It's an homage done flawlessly through and through.
Second of all the movement and general feeling of controling the characters is smooth, requires moderate precision and, again, is literally just classic Castlevania, with maybe a touch of polish/speed I noticed - it doesn't feel quite as sluggishly methodical as CV1/CV3.
Boss and enemy design is very fun and filled with some more modern sensibilities than you'd find sometimes in those old 8-bit Castlevanias. Bosses are on average better telegraphed, there's no DPS racing to kill them before unavoidable damage kills you (which tended to happen with the old games a bit), enemies are also well telegraphed but the player also has much more tools to deal with different situations, so everything feels very nice and clear. It's all about execution, no guesswork and trial and error required more or less.
Stage design can be a miss sometimes, but it's never really bad (worst I can say about a stage in this game is that it's mildly annoying and averagely interesting). Alongside stage design the game has branching world design which all converges into the same goals/ends, so there's a lot of forks in stages where utilizing the correct character and managing resources accordingly will get you shortcuts through the stages. There's some nice signs/pointers of where to try and locate shortcuts, while others are left to the player to discover.
And finally the length of the game is quite short, which makes sense since all 8-bit games were short, the only problem being they were artificially difficulty at points to prolong gameplay. I'd say this is very much a "short and sweet" type of deal, but there's also unlockable extra difficulties (which I will get to playing when I get the itch to replay the game) which can boost replay value and give the game some of that Classicvania brutality back.
I have to praise the final boss checkpoint as well - it's a very modern and momentum-keeping checkpoint with a free extra life every time a life is lost, meaning that once you're there it's only that final duel that's left. Castlevania 1 had a similar checkpoint (although lives did nothing on it since it had infinite continues and the only checkpoint was Dracula himself there), while Castlevania 3 was brutal with it requiring a replay of the whole final level if lives were lost on the 3-phase Dracula showdown.
All in all it's a pretty flawless game imho, but not in the sense that it's the best game ever, rather in the sense that it just doesn't have any visible flaws - it's presented great, it controls nicely, it has good system design and it's very focused on what it wants to achieve with some added replayability with the stage-forks and unlockable difficulties.
It's a very good modern take on a classic Castlevania game and it's a joy to play, but it also focuses so much on being like Classicvania that it doesn't really do anything too special (yeah the character switching system is different and more robust than CV3's, but it's still the same idea at the end of the day).
It's really just a love letter to Classicvania, and I'm glad Iga did a classic title instead of a metroidvania, because that signature gameplay style that the older ones have isn't something we see often, but metroidvanias are literally everywhere atp.
