I know it's already too late for this, but I really wish they had cloud saves. My save file got corrupted so I had to start from scratch. It's a really cool game featuring my favorite Hyperdimension Neptunia character, but the lack of cloud saves makes it hard for me to restart the story. It's something to keep in mind in case the same thing happens to you. Anyways despite its flaws, I had a really fun time playing this game.

TLDR: The game is decent enough to get a kick out of if you're into Neptunia. But, is overall lacking.

Gameplay:
The game had some interesting ideas that resulted from adapting the elements from the mainline games into a Strategy RPG format, but after a while, it felt less about "Strategy" and more about spamming the highest damaging move. Your equipment and placement doesn't really matter much when you're just spamming your best AoE move and the enemy is doing the same thing. The endgame content also felt pretty mindless to play, and the most I got checked by was the dragons on that last S rank mission, of which all I did was brute force it with elemental gems, which was enough to clear it.

Another thing is how slow things are. After playing for a while, it got really bothersome to select a character, select move, go to the space I wanted the character to move and then select wait. It doesn't sound like a lot, but when you're doing it for EVERY turn, it starts to build up your impatience. And that's not considering that when it's the enemy's turn, the game has to go to where they are to show you that they did nothing that turn, go to the next one to do the same thing, and repeat until it did that for every enemy on the map. Again, doesn't sound like a lot, but it really built up.

My last gripe with the gameplay is the map design. While some of them were fine enough, some of them had the issue of being too long, or too elevated. This game has limitations with movement, and some maps are designed around said limitation, but not in your favor, it's against you. Only the player units are limited by things like terrain effects like the shock floors in Lee-Fi's map, the pitfalls in Lid's map, the Conveyors that are on a lot of other maps, and so on and so forth.
This seems like it'd be naturally a disadvantage to the player, but a lot of these should also hinder the enemy, and there's no real reason why they should exempt from them. This probably only bothers me due to the fact that I also play Fire Emblem, and enemies there are also affected by these negative terrains.

Other than all of this that I mentioned, some maps are just plainly not very fun to play due to being too gimmicky in a bad way that limits how you approach situations, and others just make me think "How can I cheese this map to not play it?" Although, that can be a good or bad thing depending on how you look at it.

Story:
On the surface, it's enjoyable. It's what you'd expect from a Neptunia game, although I will say that it's really watered down due to how the story is structured.
When you think about how the story goes after the first few parts, it essentially becomes "Go to this place, talk to the General there, have a scuffle of some kind, the general joins you." It's like that for the majority of the story, and honestly, a lot of it feels like filler.
There was a bit of drama at around the middle portion of the game with Noire becoming more "tyranical" which, kinda felt stupid, but I just ignored it because I was at a point where the gameplay was starting to make me numb to everything else.

It may sound like I didn't like the story, but it's just that I didn't find it anything special, especially when compared to other Neptunia spin-offs. It's still fine enough to enjoy it, especially if you like Neptunia.

Characters:
I enjoyed the quips and banter that the characters had in the story, even if the player character, the Secretary, didn't add much to it. However, I believe that the game massively struggled to really make you enjoy the characters because of the sheer amount of them.
Characters like Little Rain, Vio, Wyn and Generia G had barely any presence in the story due to being characters that join towards the end of the game, and don't have a lot of time to make any strong impressions outside of the 3 story cutscenes that are focused on them.

There are side events that can be unlocked by raising Noire's Lily Ranks with the Generals, and while they do a good job at giving more of these characters, they still don't make full use of what the characters could offer and are generally very one note. I know that I honestly can't expect a Neptunia game that isn't the original PS3 release or a Nepgear focused game to give me any depth and nuance to the characters, but I at least expected more jokes regarding a lot of the characters' quirks. And in that front, I am a little bummed.

If it means anything, Estelle is my favorite character from this game, I played Tokimeki Memorial because of this game, which lead me to enjoy Saori more than before, Ryuka is pretty good as well, and Sango managed to gaslight me into thinking she had more screentime because of how much presence and strong personality she had.

Other stuff:
I did my first playthrough on Hard difficulty. It didn't affect much other than the final boss feeling extremely unfair, what with her having insanely high stats and insta-killing attacks that I couldn't do much about. I think the game expected me to make use of the huge cast of characters to overwhelm her with numbers, but I kept going at it with brute force and eventually I won.

I personally haven't had any game-breaking issues, but a lot of people did have them by the looks of it. If it helps, I played the entirety of my playtime on windowed mode.

I did get every achievement, which is something I wouldn't wish even on my worst enemy. It's a hellish nightmare of a grindfest for Lily Ranks. There are way worse games out there, but out of every Neptunia game, this is easily the worst one.

And to close everything off, I gave this game a "Not Recommended" because I felt like the game was lacking. However, I believe that the "mood" you play a game on will heavily impact your enjoyment of a game and how you ultimately feel about the game as a whole.
I played this game after being burnt out of playing other Neptunia spin-offs that I consider to be a lot better than this one, so that may or may not have impacted my own enjoyment of the game, and how I view it in retrospect, even when looking at it in a vacuum.
I also hunted for every achievement, which left me with a sour taste due to the unholy grind for the Heartthrob achievements.
My point is, if you still decide to purchase the game after scrolling through reviews, or if you looked at reviews after having played the game, make your own judgement based on how you felt while playing, and try not to let others sway how you feel about it.