I love(d) playing the board game Hero Quest and this is the best "add-on" one could possibly want!
It looks good, it's easy to learn, you can take it easy or try to run through all the quests...
To me the best part, a true relieve, is that you can play whenever you want, without having to consider guild related "must-do's" on specific times. And without the need to play with or against other players in order to access certain game options.
Why not 5 stars? These mechanics work fine for board games. But this is digital... It must be possible to add some nice extra's that reduce the repetitive nature of the game a bit. Create a tavern, training area and marketplace that actually look like a tavern, training area and marketplace.
And though I truly love the fact that you're in no way depending on other players, it would be cool to interact with them. Exchange experience with each other, create a scoreboard for achievements, highest damage dealt, stuff like that. Preferably within the tavern