Short Version:
It's more of a fun game with some tits on top, rather than an H-Game with some gameplay inside. It's just an old-school Castlevania game. Try it out, buy it on Steam (or here, if you do not want it showing up in your account).
Long Version:
Pros:
+Really fun. The map design is pretty convoluted, but pretty good. I did get stuck in the later half, going in circles, but I feel like that's more of me being dumb. I think.
+Graphics are good. It's pixel graphics. You obviously know that, if anime/pixels are not your thing, well... Yeah. Bosses are pretty detailed.
+Controls are good. Placed on keyboard. It's simple enough that you can easily get used to it.
+Plenty of variety. Just like in Castlevania, there's a variety of sub-weapons to use. Though, the cross that tracks enemies and the bomb are probably the two most powerful items, so...
+H-Scenes. Pretty good. It can look a little bit weird at times, but honestly, I do believe they're pretty serviceable, if you're interested and fine with pixel tiddies. Also, press H many times on the main menu to unlock the gallery, temporarily. I don't remember how many times; just keep going till it unlocks (or it might be IN the gallery. It switches between Libra Heart's games, so...)
+Quite a bit of variety in bosses. They are also decently hard.
+It's pretty long. Maybe 3-4 hours of gameplay? Maybe more?
+Music is pretty good, actually. The boss music is pretty good, NGL.
Cons:
-Pretty easy to softlock the game. If you die, and pause the game... Yeah, gotta quit out and play again (unless they patched it in DX version. I played the older version).
-Once you get Succubus form, it pretty much outclasses human form in every way. Base speed is faster, the fireballs just do more damage. You jump higher, etc. Of course, human form will have sprinting and stuff... Also, there's a glitch where if you start sprinting, crouch, and transform, you maintain sprinting, but with Succubus' speed. Again, at least in the old version.
-It can get annoying to try and 100% the game. If you're a completionist, sure, go ahead. If you're a casual goer, good luck getting all H-scenes. Not that it's impossible, just annoying.
-H-Scenes are pretty limited. Mostly, if not, all are rape & vaginal. Maybe a gang, maybe not, with beasts and whatnot.
Overall:
Good. It's a really fun metroidvania. I'd actually buy it on steam, if it wasn't a hentai game. I'd even leave a positive review there too. But, well... I'm not going to, because, well... Yeah. If you're looking for actual gameplay, yep. This is the game, here. Play it.
Looking for hentai? Well, take a look. If it suits your tastes, spam H on the main menu, until you hear a noise.