Mark of the Assassin is DLC that came out a few months ago for Dragon Age II. It features Felicia Da as the skilled elf rogue Tallis and offers a much needed excursion from Kirkwall and your first ever visit to Orlais. Depending on the characters you chose to take with you (2 as Tallis is mandatory) they will also comment on how nice a change of scenery is.
For me personally I think that Dragon Age II's decision to make a story set primarily in one big city and focus on proper character development of not only your own character but your companions including a never really done before family take, was superb and well executed. I never felt to claustraphobic in Kirkwall, but for DLC I welcome a nice visit to some grassy, mountainous plains for a break.
The game intergrates the story with the Seeker enquiring about Tallis and the events that seemingly caused serious strife in Orlais, from Varric. This helps to weave the DLC into the overall game and story nicely.
You meet Tallis in Kirkwall after an ambush where she enlists your aid to help her steal a relic from an Orlesian estate. The Orlesians are basically French and pretty much all of them sound or act pompous. Duke Prosper seems to be the only one that is taking everything in his stride, but we find out later on why he's so cheery.
Your first goal in this story is to hunt and kill a Wyvern, which Merrill will comment sounds like a cross between a cistern and a wife. For me I could stop thinking about Wynne with fangs. To lure the Wyvern you'll need to collect certain things, like blood or steaming Wyvern dung. It's a lovely sight to see the Champion elbow deep in cack. Depending on how many items you collect you can then bait a regular Wyvern or a more impressive Alpha one, though they both look the exact same. One is harder to defeat and if you lure the Alpha it will net you an achievement over the regular Wyvern.
Once that has all been done you will gain entry to an outdoor banquet held on the estate and hosted by the Duke. There you will have to find a key to an entrance to the estate in order to find this relic Tallis is so desperate to get her hands on.
You'll bump into some characters from the main game and depending on completed quests, will receive different dialogue. For example you'll meet the rather ditzy Comtess de Launcet who was feature in the Act III quest On the Loose, where you had to retrieve her equally stupid mage son.You will Bann Teagan from Dragon Age I (who's sister was Queen Rowan of Ferelden).
After some running around to get the key, you're inside the estate where the game takes on a Splinter Cell style approach. You must try your best to traverse the grounds covertly, with distraction techniques such as stone throwing and a good whack to the head being your only form of 'attacks'.
After you get so far, things will take a turn and while the main reason you went to Orlais will still be important to Tallis much more pressing matters, like escaping and getting through dungeons will be your primary concern.
The end of the DLC results in a boss battle, that depending on your opinion of the boss, will end in satisfaction.
The DLC offers a great temporary companion in Tallis, who's long distance knife throwing skills are extremely useful and her dialogue options and the interactions between your other companions are fun and well matched. Felicia Day gave a great performance and I would have liked to have had Tallis as a permenant member from then on, but Tallis has her own matters to attend to after the events at the Estate.
Barber events eh
All in all this is a nice addition to the Dragon Age II game and worth the price. Bioware produces a lot of DLC for their games, for the most part they do an ok job but with this I think they did quite well, brief as the game is. You can net all the achievements in one playthrough and there are some exclusive items to be got here as well.
The story taking place in one location didn't detract from my enjoyment of the game, at all. Like you, I thought it was well executed. I still consider the original Dragon Age to be the superior game out of the two, but DAII was a nice change IMO. I'll have to mark this DLC down for future purchase.