For those unaware, Neptunia is a franchise that has been running for quite some time. Starting with Hyperdimension Neptunia, there have been a ton of games featuring the characters introduced there. There have been RPG's, a Strategy RPG, a Musou game, and some others I'm forgetting off the top of my head. The games don't necessarily connect in terms of their narrative, but simply use the same characters for different stories.
If I were to point out what the defining aspect of the series is, it's that it acts as a parody of whatever genre the game is set in as well as poking fun at the stereotypes of its own target fan base. It's not in a mean spirited way mind you, and so long as you aren't overly sensitive about having a stick poked at you from time to time you're likely to get a good laugh at the series humor. There is more to it than that, but I think that gives you enough context to dive into their latest offering.
Super Neptunia RPG is a 2D RPG with references and callbacks to the old days of gaming, before 3D was a thing. Our hero Neptune has amnesia, and when trying to recover her memories she gets involved in a fight between The Resistance and Bombyx Mori. Bombyx Mori acts as the game's antagonists, and they are trying to prevent the development of 3D games and forcing developers to make nothing but 2D titles. With this premise, I think you kind of get how meta the game can be with its plot.
This is kind of where the game starts to fall apart for me, and I'll get to how the actual mechanics work in a moment, but it doesn't really feel like the game commits to its own premise. While all the graphics are 2D, as well as traveling the maps and dungeons having a feel of old 2D games, the actual RPG combat draws almost nothing from the 2D feel of old, and instead feels like it draws heavily from two 3D RPGs specifically, Final Fantasy IX and Final Fantasy XIII. From IX you have the system where you learn new abilities from equipment, and only have so much space for equipping passive abilities based off your level, and from FF XIII you have the Paradigm shift that was used for swapping 'classes', though in Neptunia you're just swapping abilities. Without spoiling much, the world you currently live in is suppose to be ruled by the premise of being 2D, so it feels a bit odd when the actual combat feels nothing like that era.
Even the story itself fails to really commit to the idea of 2D vs. 3D, as only Bombyx Mori has this complex that 2D is simply better, whereas most everyone else in the world seems like they would be fine with both co-existing. Even then come games end you find out it's not even really about 3D games at all.
As far as the actual humor goes, I'm a bit torn. It can be funny, the references are pretty well done, and it can be pretty on point at times and all done in good humor. That said, despite only having played a few of the Neptunia Games, it kind of feels like the same stuff I've seen in other games of the franchise. With a couple of exceptions, one being an absolutely hilarious joke involving a rather detailed dating simulator I won't spoil, the game was mostly just consistently amusing without any really big laughs. As the biggest reason to follow the story, I would hope for a bit more. If you are already familiar with the series and aren't that tired of its humor, you're likely to get a lot more out of it. For me, it feels a bit too similar, and while I enjoy it I don't think it's enough to carry the game from a story standpoint.
That leaves the actual gameplay, which bounces between needlessly frustrating and mindlessly easy. The actual platforming and traversing the dungeon is the frustrating part. Not because it's challenging, but the controls aren't always very responsive. There will be times your jump just doesn't feel like it is responding to your input, which can make avoiding contact with enemies you don't want to fight or even jumping over a pit obnoxious. I've read a couple of people having issues with that on PS4 as well, though I'm unsure if it's an issue on PC. Take away that issue, and the platforming itself becomes simple.
Combat is a bit hard to judge because I honestly don't know how much of it works. I have beaten it, I have beaten some of the optional hunt bosses whose recommended level was quite a bit higher than mine, and I did all this without ever once using any the games break attacks, and by the time I even remembered they were a thing I forgot entirely how to activate them so just... didn't. They are character specific attacks that can be activated, or apparently, there is an attack that can be used by all four characters if you fill the gauge completely.
The game, like classic turn-based RPG's, also includes status effects. I have no idea what most of them even do. I only know that one of them turns all your actions into 'normal attack', and it took me a while to realize this as I so used to barely paying attention to the actual combat, but you can simply open the menu and use an item to quickly get rid of any status effect. It's so quick and easy it feels more like a nuisance to swat away then an actual problem.
That really is the main issue with playing this game, I managed to clear the story as well as a fair bit of side content without having to so much as pay attention to what was actually going on in the battle. Spam an attack the enemy is a week too, occasionally heal. Rarely does anything come up that gives you need to alter this formula, and even then it's barely any more than that.
I hate anytime I have to give so much crap to a game released by Idea! Factory, because they are one of the more interesting companies in gaming right now. They release games with all kinds of strange and interesting ideas, and they tend to give me releases that add some interesting flavor and variety to my gaming lineup any given year. At the same time, the quality of their releases can feel a bit all over the place, and this one sadly falls on the poor end of the spectrum.