Review from someone almost finishing the whole game:
the actual game is alright and was relitively easy for most the game untill the upstairs and the final part.
The room with the sucubi where you get the blue gem is an extreme difficulty change from it being easyish to a practical instant death. If i were to change one thing in just that room id just remove the middle enemy. Asside from it being very hard it certainly is not imposible and does have a checkpoint close by to retry.
The main issue i have is the final boss. Along with the blue gem room it is hard yet not imposible and certainly time consuming. After that room i thought i was done and this is the part that made me not want to finish the game and that is the boss battle continued out of that room and although it isnt extremely time consuming to get past it is still extremely difficult and you do not get a checkpoint meaning if you did die you would have to redo that last part once again. I am sure eventually i could beat it yet it is such a ridiculous ending i am not going to do it again. I would stop the boss from excaping or set a checkpoint outside the door.