I wasn't even completely through the game when I decided to buy the dlc (waiting to play it after my first playthrough of course).
Now the Back Alley Brawl is a great dlc component; it lets you slaughter til your hearts content, or until you die. Well, I just played through 55 minutes of death before being killed while stabbing a tallboy (cheap kill npcs, get some skill! QQ).
I did a No powers, no HUD, Ghost, Pacifist play through, and I have videos. The bloody Dunwall Tower especially inside was a horrendous nightmare to do without using blink but after a sleepless night I managed it, the rest wasn't any difficult even without the HUD for aiming if you've done 3-4 play troughs with it on. I absolutely love the game, I should get around compressing and uploading the footage to youtube
The epic thing which I noticed is that if you are never seen/ killed anyone and hide properly all the unconscious bodies, nobody knows who you are, the posters around town will mention Cambell being expelled from the order, Sokolov disappearing etc. but there will be no mention of you. If you aren't discovered but bodies are found the posters will contain a silhouette with a question mark as well a price for your capture. If only a single guard sees you the poster will have a picture of Corvo with the mask ok. Further more if you sign the guest ledger in Boyle's manor you will later find a letter belonging to Burrows which will say that some imposter is pretending to be Corvo. Brilliant, brilliant game. Trials of Dunwall city is rather meh, I never liked arena-focused DLCs, but The Knife Of Dunwall and the whole Daud gameplay is brilliant albeit short
If you haven't already, ask the heart about Piero and wait for it to talk about him and baths. Eventually you hear of Callista taking a bath and if you take a look around, you can spot Piero.
I was a little confused about the ending of TKOD, I guess I wasn't quite paying attention. Probably focusing too much on Delilah.
I've been listening to various soundtracks while doing the brawl; it's so epic when Lux Aeterna kicks up just as you slice some dude in half.
Also, time stop is glorious. I stopped time in the Boyle party and pulled out my crossbow. It was like something out of the matrix.
...and if you jump in the bath with Callista the mission will fail, saying the conspiracy is dissolved due to insurmountable differences. The DLCs end is weird because the last one will continue the story The Glenblah-blah Witches