I'm a consumer of single-player DLC, especially when it's story-driven. And I must say, I've been disappointed with a lof of recent SP DLC for a lot of games. DmC comes to mind with Vergil's Downfall, Dead Space 3 too, and recently MGRising with Jetstream Sam's chapter. All of these DLC's cost about 10$ and roughly takes an hour or two to beat, with a lot of re-used environments. Even though playing around with Vergil and Sam was cool, you visit mostly re-hashed levels with the same old stuff. And in the end, I didn't felt very satisfied with either. Same for Dead Space 3.
When Knife of Dunwall was announced, I almost decided to skip it. Almost. And glad was I wrong to give it a chance. Not only do you get three fully-fledged missions, two of which are huge and open-ended, you also get new powers and much-needed stun traps and grenades. Daud comes fully voiced and fully loaded with his own back-stab animations. The whale factory is such a gorgeous level, if a bit gruesome. You'll get the same kind of objectives you've had before, tons of different paths, hidden stuff and of course, alternate decisions on how to proceed.
I'm roughly 4 hours in, and I'll probably beat it in two hours. If you like to plan, to stealth around and whatnot, you'll definitely get your money's worth. This DLC really, really ties to the main campaign and nothing feels out of place. I can't say enough how happy I am to visit new environments, especially when most developers prefer to re-use the same levels for their DLC content.
To those in doubt; don't. It's almost a small expansion pack. Almost. And for ten bucks, you'll get a great set of levels. Alongside Alan Wake's DLC, this has to be the better piece of DLC I've payed for in a long time.