DD2 is kind of an odd duck. It is VERY different from DD1, roguelite instead of pure rogue like, one fixed team instead of dealing with a team... And SO. MUCH. CONTENT. The game has been reworked, revamped, polished, completed a number of times... And I think always for the best.
A good balance between creative mechanics and classic stealth/infiltration games. Not the hardest there is if you're experienced in the genre, but I guess that's also part of the appeal. It's nice to have a great game that can both please completionists and beginners alike