The first time I tasted grass-fed beef (which we raised 8 years ago), i thought the steaks were gamey and tough. The hamburger was very good and lean. I think grass-fed is an acquired taste (like rare tuna).
How you cook it makes a big difference. Grass-fed is leaner and you don't need to cook it as long. It gets nasty if you cook it over medium.
Over time, I have grown to prefer grass-fed. Not all grass fed is raised correctly (or eats grass their whole life). To me, corn-fed has a bit of a sweet taste.
I found some good articles about the health benefits of grass-fed beef (from HIH, Mayo clinic, NYT, etc):
http://kindbeef.com/benefits-of-grass-fed-beef/
