Overall I like the game, albeit it's easy to improve because there are many things that could be added it is nice enough.
Things to note is for example that there are too few futa enemies, I would have liked a few more to tell the truth and at least a heroine that was or could be a futa.
The level drain isn't truly fun in this game, mainly because it easily becomes like a chore, too many characters to give them levels. Albeit I have to admit that they are easy to farm, but still... it's a chore, even more it would have been nice that enemies could get stronger by draining you in the sense on future fights too, overall it was kind of funny the cow succubus fight that increases his breasts by getting your levels, it was a nice surprise compared to other fights.
As I said a nice game, with more potential to give but unfortunately we won't get to it.
Leaving that aside a few tips for new players:
-Medals are important, you should focus on getting aegis (fake), excalibur (fake) and stat up items in the shop. Overall with the fake ones you can end up making the real ones in the blacksmith.
-The blacksmith girl is the most important character to level up, to get the best items you need to level her up, overall because you will get your levels drained there are only 2 main ways to get stronger, the first one is stat up items which refer to using medals and the second one is to actually get better items by making them at her shop.
-For those that are curious, the Harpy girl can become a companion in new game +, you just need to get one of the endings (after you get an ending you reset to before you get it and appear in the house, then you will find a letter just outside the house about a phantom thief).
-Colette is a character that I personally recommend to get her ASAP, her passive ability will make you farm levels more easily so be aware of it (basically it reduces the cost to defeat enemies, really useful), even more you will optimize her use by grouping her with the mushroom girl that gives you a chance to get double level up.
-To farm money really easily I recommend getting the item nanako underwear. You can get it by having a lot of sex with nanako in the brothel, overall this object makes it so that each time you get an item on the floor you find money too, that's the main use it has.
That's mostly it, have fun.