Oryx: Here's what I see, from my limited 20K perspective.
The upper part of the B group is clearly alive; even if W whittles down the top, a, b, and c are miai to make eyes. So what's the best that W can do?
W can't completely separate the bottom group from the top, because y and z here are again miai, but both for B to connect to the strong top and for W to connect to the lonesome .
Also, I don't see any immediate threats against W that she has to defend against.
I'd say the best that W could do in this case is reduce B as much as possible, not seeing any super threat, is E3, threatening the B groups and forcing him to answer in gote.
Dieter: You're close. You have the move, but should put less faith the apparent strength of Black's upper part.
AdamMarquis: After , black needs a and b to get an eye on the lower side. If black plays c, White can push at d. If Black blocks, he still only has a straight three, and is dead. If Black plays d...
I think, therefore, that black is dead. He does have, at my count, 5 ko threats to live. 3 from playing as in my diagram, one to make an eye on the bottom, and one to cut off the two white stones. Depending on what is "off-screen" to the right (like a strong black group), perhaps he has more threats to escape?