I played around for three hours now. In its current state Book of Hereos is… “okay”… if you’re looking for quick dungeon crawling action inside a traditional medieval fantasy campaign setting. But people who are looking forward to a deep, overarching plot without knowing what the game is all about will be less than thrilled by it.
Is it perfect? Certainly not. But being somewhat active on their discord, I can tell that the devs are currently hard at work addressing numerous bugs. From what I saw the update is pretty much focused on ironing out gameplay issues. Although I do hope that they will make the game run a lot smoother. The optimization isn’t the best you can find under the sun…
That said, I do not regret purchasing Book of Heroes. I adore the environmental design of the various dungeon tilesets and find the music to be both pleasing and fitting for the Middenrealm. But I can do without hiring the mercenaries… solo is where the fun for me is. Others might be more at home with co-op instead.
It was also a very nice gesture of both the developer and publisher to lower the price on release date. Initially it was priced at 29.99 EUR after all. Imagine my surprise to see that this was reduced to 24.99 EUR. Things like that make the devs really sympathetic in my eyes. 
What I would like to see from Random Potion in the future are more crafting blueprints, refining the gameplay, bug fixes and improved performance. Also: a level editior for creating our own dungeons would pretty much guarantee its success. At the very least inside the humongous TDE community. For the casual RPG crowd on the other hand… not so much.