Back in the late '90s, biologist Joe Staton did a comparative study of the tastes of different animals for the Annals of Improbable Research .
His hypothesis was that the relatedness of tastes of animals is correlated to their evolutionary ancestry.
You can read an abridged version of his article here .
Looking at the phylogenic tree at the bottom of the article, horse meat has the general flavor of beef and is most closely related to deer (venison) and American buffalo (bison).
In my experience, horse meat is like a cross between venison and beef.
Edit :
In case anyone was wondering, human apparently tastes like pork.
cooking.stackexchange.com/users/5600/ESultanik
Horse meat is dark red and usually quite lean.
The risk is to overcook it and end up with tough meat.
This probably has to do with the fact that most horse meat is "recycled" animals, that's to say horses that were not bread for meat and
that spent a part of their life working.
In my part of Italy (Parma), we also eat it in its raw ground form (like a steak tartare ).
The traditional presentation is ground fine, spread on a white bread, salt, pepper, lemon juice and a drop of olive oil.
Garlic also goes well with it.
Horse meat is less likely to host parasites that are harmful to humans, so I wouldn't be too disturbed by the thought of eating it raw - and it does taste great.
A filet americaine with horse meat would probably taste very good too.
Here is a recipe for picula 'd caval , a sort of horse chili from nearby Piacenza http://italianfood.about.com/od/furredgameetc/r/blr0881.htm although I would not cook it for quite that long, to avoid having tough rubbery bits at the end.
For the same reason, reheating horse meat is usually a bad idea.
Here is also a discussion about the true recipe, but it is in Italian http://www.coquinaria.it/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=6;t=000843;p=0 of course every family has their own version and of course it is a point of religious faith that that one is the only true one - after all it is Italy.
cooking.stackexchange.com/users/4558/Walter A. Aprile
Like a filly cheese steak.
I'd hate to saddle you with a bunch of recipes.
Good with stallio-- scallions.
Careful, frying it, since it tends to be a bit tempermental.
Leaving now.
cooking.stackexchange.com/users/1443/Ocaasi
I've had it in Italy as a child - I was actually told it was beef so that I wouldn't ask questions.
The big differences are that it is leaner than beef, and has a coarser texture.
cooking.stackexchange.com/users/5800/Debbie A
It tastes like whale meat :)
It's a red meat, with a characteristic texture.
Personally, I like it a lot, but it's difficult to find if you are outside of Italy and France (as far as I know).
You can use it as a regular steak, instead of pork, for example.
Pork is more delicate as a taste, horse is more intense.
cooking.stackexchange.com/users/1342/Stefano Borini
Horse meat is often consumed in Mongolia, especially during the long cold winter periods; it contains a lot of nutrients suitable for winter.
It is very lean so its good to consume when cold, meat is quite smelly while you cook it
but once it's done it is a good substitute for beef, and of course it contains a lot of collagen.
cooking.stackexchange.com/users/63175/guest
What (roughly) does horse meat taste like?  What kind of dishes can I make with it?
Uses of Horse Meat
cooking.stackexchange.com
<meat><culinary-uses>
cooking.stackexchange.com/questions/4387
cooking.stackexchange.com/users/53/Willbill
Horsemeat is leaner than beef with a coarser texture, and tastes like a cross between venison and beef. It can be eaten ground or as a steak, and can be a good substitute for beef. Horse meat is very similar to steak. You can cook it as you would a steak.
Horse meat is very similar to beef, but it is leaner and has a courser texture. You can cook it as you would a steak or eat it raw as a tartare.