I've played this almost all the way to what I believe is the gate towards final boss. Gonna keep this spoiler free for those who might want to know more details about the story on their own.
English aside, the game is pretty well constructed. I didn't encounter any bugged events or severe soft locks. There was one spot where the ending text exceeded the text box but I forgot where it was since it was a one-off. I do like that most of the puzzles actually do give you hints to the correct solution, just gotta look.
I did come across a few glaring issues. And they definitely hampered the game experience.
- When the game is darkened for effect, it often becomes too difficult to see reasonably. I'm sure there's a way to lessen this or change the effect so it's less intrusive.
- A late game puzzle involves an invisible maze. This was an absolute slog. I actually put on the "no encounters" accessory because of how frustrating it was to navigate. Followed up with the fact this is a puzzle without hints and you will thankful for having that cheat accessory if you do have it.
- When there are periodic extra effects active, like sounds or lights, the game definitely slows down some. And they never really added anything to the environment.
- The game balance is in serious need of adjusting. Even cheating in level 99 about halfway through, I had problems. I'll go into more detail on this later.
- While there is breast and ass expansion for several scenes, it's only one or the other depending on the succubus and very rarely is it ever more than one growth and is never more than 2. This makes said growth rather disappointing if you're playing this game for said aspects.
- The level drain mechanic, while fitting for the context of the game, makes bosses a battle of speed and luck. If you get drained too much, the battle becomes unwinnable. This is true even after the aforementioned level 99.
Regarding the game balance, I don't think the author actually played through this game normally. Level 99 should have given me enough stats to reasonably deal with whatever was in the end game without much challenge. Sadly, the bosses are so very stat heavy that level 99 alone will not be enough to just deal with them. While I can forgive this for a game like Final Fantasy, where the game length actually makes it reasonable to reach level 99, the grind required means you're devoting time to getting your level up to a safe value before fighting a boss. And later enemies tend to be less than fair.
I also want to call out a late game boss being able to heal for more damage than I could do in one round at level 99. I'm sure the game author knows who I mean. This further exacerbates the speed/luck problems of boss battles.
Furthermore, while I have a tendency to explore thoroughly, I can tell that it's your biggest source of gear and being able to compete. If you don't explore, you can miss an important upgrade that can make a huge difference in how successful you are. The shops offer almost nothing useful long term, and that's another major problem.
All in all, despite its flaws the $7 price tag isn't too bad. I would like to see the later game enemies toned down considerably, since I don't think giving the Hero more stats would be enough compensation for the problems. And I would also like to see more growth from the succubi, particularly if you let them drain you repeatedly in combat without actually being defeated. Getting these changes would make it very worth the price.