Hi John,
2 things come to mind. First is your water. If you have hard water, you'll end up with a problem. Did these kits have grains you steep? This is often a problem because people tend to use tap water to steep with (and a lot of it) which keeps the pH very close to 7 (neutral) which in turn tends to pull tannins from the grain husks, and that will give you a nasty bitter aftertaste in beer (it's almost metallic). The solution to this problem is to use spring water for steeping and only 1.5 quarts per pound of grain. Never heat the water hotter than 170F. And never squeeze the steeping bag... that can force the tannins out, too.
Also, if your water is hard, it will effect the way the hops react with it. Hard water is bad for light beers. Think soft water and pilsners, hard water and stouts (Guiness). If you have to use the hard water for brewing cut your bittering addition in half, and see if that works. You'll get the hang of it!
I hope this helps.