Eh. This is an alright game in the series. Definitely not the best, but it did alright. I personally enjoyed the story to it (I'm a bit of a sucker for cheesy storylines).
I think the only real gripe I would have with it is the BS RNG. In order to get some trophies (if you're a Completionist/Trophy Hunter), you need to do specific events in order to level up the affection level with each Vocaloid. This game's RNG in order to get the items in order for that to happen, however, is the most garbage I've seen in a game, excluding gacha games.
The tracklist for Project Diva X is quite small, only coming in at about 30 songs (24 standalone songs + 6 Cloud Medleys). Personally it's subjective as there's a handful of fan favorites in there (The Lost One's Weeping, Solitary Envy, Streaming Heart, etc.) with some absolutely solid song mashups in each Medleys.
For what the game is, it does a very good job as a Project Diva game.

I heavily advise against trying to go for this game's Platinum unless you enjoy masochism (like me).