If it wasn't obvious enough, this game features a lot of loli so if that's not your preference then this isn't the game for you. For those who love loli, on the other hand, this game has a lot to offer in terms of sheer content.
Naedoko Demon's Ground is a game all about experimentation. It uses a monster party system very similar to what you'd find in an SMT game. Instead of negotiating with monsters, though, the main character, Eliza, must first be impregnated by an egg after which she then gives birth to a monster at designated birthing spots. The most common way to obtain eggs is through obtaining them as item drops, though Eliza can also be impregnated as a result of a defeat scene.
Perhaps the most unique mechanic to this game is the Deep World Transformation, which is available to every monster once they reach a certain level. DWT will often change the monster into useful items like powerful recovery items, equipment, or even into unique and more powerful monsters. There are a lot of monsters in the game so don't be afraid to DWT most monsters you possess, unless they happen to be very strong.
In the spirit of experimentation, losing in battle isn't necessarily a setback and can instead potentially provide you with powerful allies since each defeat scene impregnates Eliza with a monster. Oftentimes the monster Eliza is impregnated with just so happens to be one who is well suited for clearing through the current area.
Collecting a wide variety of monsters is crucial for completion as there are many side quests and miscellaneous tasks that require you to have a certain monster in your party to complete the objective. For the most part the monster you need to have should be pretty obvious, but other times it seems a bit too cryptic and you're either going to need to do some trial and error or preferably just look up a guide. I would only recommend using a guide as a last resort if you feel stuck however as I think avoiding spoilers as much as possible is the best way to enjoy this game.
Even on hard mode, this game isn't very difficult. There was only one particular fight that felt very challenging about 3/4 of the way through the game but otherwise you can auto battle your way through pretty much auto battle your way through all regular enemies past the beginning portion of the game. Your 2 permanent companions, Jupiri and Pukis, are pretty overpowered especially if you do the side quests to unlock their potential even further. Boss fights might require some thinking to overcome, but generally speaking this game is pretty easy.
My biggest complaint is that, especially if you're trying to DWT every monster in the game, this game can get pretty grindy. There is a wiki that lists all the transformation effects and I would recommend referring to that before deciding on trying to grind up a monster's level. Another thing that disappoints me is that there aren't many H scenes that feature the antagonists, at least as far as I've unlocked. It's a shame because many of them have very attractive designs and I would have liked to see at least an H scene for each major character in the game.
If you like HRPGs with deep mechanics that encourage experimentation, then I highly recommend this game. It's packed with all sorts of H scenes and the gameplay and plot are fairly engaging. Although it can be a bit grindy especially if you're trying to be a completionist, this game is very fun and has a lot of content to offer overall.