Rule of Succubus is a very poorly-designed game from top to bottom. While the art assets are pretty good (exaggerated proportions and the faces range from nightmare fuel to full derp), the engrish, overall mechanics, and even combat are lacking. What should have been a good resource-management h-game that married the concepts exceptionally, instead falls flat as a shoddily-designed cash-grab.
First and foremost, the core gameplay. While battlefuck isn't my cup of tea, the fact that your only recourse for getting stronger is to talk to the succubi and recruit them (in a "choose the right option" style that offers no repercussions for failure on the first try) is only undermined by the fact that they demand sex every other time you rest, thus draining your energy and forcing you to scrap any effort to make headway on resources and/or overall progress. The other issue is, you're not even encouraged to improve through repetition, but through a long, painstaking process of slow (sometimes, even insufferable) progress. At least with your cookie-cutter rpgmaker h-game, the promise of satisfaction exists. Here, it doesn't feel satisfying to unlock the map. It feels like a job, and, by the end of it, you're mentally drained.
And lets talk about that map for a moment, too. I've been lost, had to look at it several times, and then backtrack to another path. There are ZERO indicators of where you should go, how to get there, etc. You're forced to suffer through the poor set design and hope the path you're on is the correct one. Oh, and to even know if you made any progress, you have to open the menu. It doesn't help that enemies are generally plentiful and overtly-aggressive to the point of frustration. The worst part is, opening the map before setting up a campfire resets the enemies on the map. Actually, that's just the second-worst aspect. If you opt to run from the succubi, their sprite vanishes from the area but the game won't let you establish a campfire, hitting you with a prompt to defeat every enemy beforehand. Well, shit.
Healing items are also a major problem. I've played both the survival and easy modes, and found that in both cases, the work you put in to make a healing item hardly validates itself. Most rpg's will reward you for your study of alchemy; RoS seems dedicated to punishing you for playing the game. I wouldn't have an issue with this if there were in-dungeon alternatives in limited form that required resource-management and allowed for variety in combat, but there aren't. The combat itself outside the succubi is basically "run into enemy, watch for whichever bar drops faster." That is, the combat is hands-off outside the "battle-fuck" aspect, and even that lacks any real player input. As stated before, too, you're encouraged to improve via "team-mates" that will cripple your overall progression at every chance they get.
Finally, we move onto cg's. Honestly, there are maybe a couple succubi with any appeal cg-wise. As previously-stated, the actual character designs are rather exaggerated in their proportions and, while this isn't exactly a point against it, the lack of variety for each succubi's cg is. There are also no consequences for losing a fight, so it robs the player of any agency in these situations. If you lose, you're "rewarded" with a short cg/text loss scene, and then tossed unceremoniously back onto the beach you started on (or wherever your respawn is). At the beginning of the game, we witnessed a sailor drained of semen and life-force, so it's jarring for the game to go from "succubi are dangerous and you should avoid them" to "they'll take a moment to sexually assault you and then unceremoniously drop you in a safe zone so you can catch your breath and try again." At this point, you no longer have any reason to be invested in this game and everything becomes a Sunday chore that you're doing just to get to the end.
Overall, Rule of Succubus is just "meh". It had great potential to be part of a genre while setting itself aside in terms of character design and gameplay, but feels incredibly rushed and poorly-programmed. Anyone interested in giving it a try can do better and should skip this trainwreck lest they find themselves among the debris.