It's ages ago that I had it. It is more bitter than beef, a little like game meat, and very lean. You definitely have to chew much harder, no meat for people with no teeth .
This is the reason why in Sauerbraten the meat is in a marinade which contains vinegar - after that it is soft like Justin Bieber!
It traditionally was a poor man's dish, as horsemeat was quite cheap in the times when there were many work horses around.