I've only played Mk2. I know the combat system is different than the first game and that the Rebirth games all use the combat system pulled from Mk2. The combat isn't horrible, but the game acts like you're doing some advanced sort of gameplay when they just shoehorn you into repeating the same stuff over and over. Basically, use a break combo, then use an attack combo, maybe use some skills in between, repeat, over and over. During any normal battle, it was wait the first turn so and so far away so the enemies move towards you, then move towards them so all three of your characters can strike first. It's a TRPG type combat system that uses the Breath of Fire Dragon Quarter/Arc the Lad Twilight of Spirits style of combat. The combat was the best part of the gameplay but when everything else was so much worse, an okay combat system can't salvage everything else.
One good aspect of RPGs is exploration. All of the dungeons in the Neptunia games are small dungeons where exploration is practically non existant. It takes two seconds to move from one end of any dungeon to the other end. The dungeons aren't exactly identical, but they may as well be the same exact thing with a different background because that's exactly what they feel like. The quest system isn't much of a quest system as instead of being unique, they're all kill these types of enemies or gather these types of items, and then they'll just start repeating themselves.
Compare the dungeons to something like Wild ARMs or Lufia 2 which the exploration in dungeons is puzzle like, similar to Zelda, giving some thought to the dungeons as well exploration, so there's a bit more depth than your average JRPG, and the dungeons to the Neptunia games are just a complete joke. Compare them to any other RPG that still uses the premise of exploration as one of its concepts, and the Neptunia games dungeons are... well... still a joke and don't add a thing to the game.
Sorry, but unless your gameplay is going to blow my mind, then you're going to have to give me something than a mildly entertaining story at points, because despite the idea that RPGs are played for their story, they're played for a combination of things. If it was story only then I wouldn't play an RPG because I can go to any other story telling medium and get far better storylines with stuff that is considered sub par in that medium.
It's nothing like Tales of. The combat is like Breath of Fire Dragon Quarter or Arc the Lad Twilight of Spirits.