Well, I can say that I've beaten and 100-percented the DLC for Dark Ages now. Overall I'd say it's a 7/10. The master arenas are fun but they do suffer a bit from Eternal's "what the actual am I looking at" with some of them and how spammy they can be. Like Eternal, you can only do so much to make the game difficult before you just start repeating the same encounters having 4-5 minibosses on the field at once. If there were any reservations on what the best weapon was, well, the master arenas prove its the rocket launcher by a country mile.
I hate the "secret" boss with a passion though and its so bad it makes the Dark Lord fight look well designed. If it's any consolation, the horrendous boss design will die with ID at least...