This game is based on DND 5e, though it's not an official DND product. There are some rule changes, but it's close enough. The story of the main campaign is kind of generic, though it does the job at giving your group an excuse to go adventuring. The character / party building and the tactical combat however, are really fun. I recommend using the Unfinished Business mod, which does a great job at implementing closer to tabletops rules, as well as adding feats / spells that didn't make it in the game. I'd say solasta is to BG3, what icewind dale is to BG2.
First, let's address the elephant in the room : the price tag. What the right price is for an niche game that took years to develop is, is highly subjective, but 40€ is a lot more than what indie games usually go for. That being said, the game is really good, with a nice story and really good gameplay. If you're a rpg / dungeon crawler fan, chances are this game will suck you in. Hard. If you can afford it, and you like those kinda game, you should consider giving this game a chance, it's worth it.