The bad tastes mostly comes from the lack of proper care of the meat as it is processed. The #1 thing that makes the meat gamey is the deer fat, if it is not removed it will taste bad & give you a greasy film on the roof of your mouth. The reason why is the body temp of cows & pigs is close to the body temp of humans. So the fat from them will liquefy at our body temp but the body temp of deer is over 100° & there fat won't liquefy at our body temp.
The time it takes to get the deer meat down to under 40° will change the taste too, every minute it takes to get the deers temp down more Bacteria are multiplying. Here is a link the explains it.
http://www.trophybagkooler.com/silentsecret.html