How dark can a romance be?

My new Kensington Zebra, To Touch The Knight, has recently been reviewed by Romantic Times. The reviewer liked it and said Compelling characters and suspenseful moments will keep readers well entertained, but added, the dark motifs and plague plotline may be too somber for some.

Fair enough, but it set me thinking. I've set my novel against the backdrop of the 1348 plague, now known as the Black Death, a time of great hardship and terror when over a third to a half of the population of Britain died from the plague. My story does have dark moments, to reflect this. However, my romance is also a triumph of love over adversity, where a lonely, troubled man and a woman who has seen too much horror learn to care again and love. Others in their company also find love and hope and happy endings. To me, such joyous outcomes make the novel a victory for life and love and as such a true romance, whatever the other dark motifs in the story.

I am fine with the review and understand why the reviewer added such a warning, but still it intrigues me.

What do you think? How dark can a romance be?

To help you decide, the first two chapters are here.