This was sold to me as sedum hakonense 'chocolate drop', but I came to a similar conclusion after some internet searching. The color is off from yours, but matches (along with the flowers) some other pics I found online:
Then again, my particular plant seems to be doing well in 10+hours of full sun with little to average water, so maybe it is something else? Maybe the images I googled were also mislabeled?
Alternately, maybe mine is unhealthy? It's stayed roughly the same color as it was when I brought it home so I assumed it was healthy.
