Dragon Age 2 - Mask of the Assassin Review @ CPU Gamer

There's an enthusiastic review of DA2: Mark of the Assassin at CPU Gamer, where they awarded 9/10 for this DLC:

Overall, I would say that this is precisely the type of downloadable content that publishers need to be supporting their products with. In the end it is ten dollars, for a 4-5 hour chunk of content that features a new party member and some new treasure, quests, and monsters. Tallis leaves your party, which is sad as she would have been a fun rogue to keep in the party.