I have not read the manga, but I have watched all of the anime. I agree with so much of what you write first, what fascinates Sebastian, what drives Ciel, the pride he has in his family and the work they have done/still do for the Crown. I never saw any hesitance or distaste for the underworld or the dirty things Ciel does, either....

How I interpreted the revelation of the Queen having been behind his parents' deaths was that he felt betrayed, yet he didn't entirely put the Queen among the simple criminals because she'd been more than the Queen, she'd been a symbol as well. So it got complicated there. He has lots of dedication though... and partly perhaps to also avenge the Queen's fate.

The words "kill me now and make it painful" looked and felt more like Ciel wanted to *feel* the end. That he wanted to experience something for himself, together with Sebastian. At least that was how I took it when I watched it. There seemed to be no guilt or feeling dirty. He felt mature... but that he saw it as that he had fulfilled everything he had to do, and since the Crown was no more, there was no one to need his services anymore... and the contract with Sebastian therefore had to be paid.

I don't know how it goes in the manga, but I was rather satisfied with the anime ending, and I didn't think it felt cheap. :)