I don't know why, but all the commercial chocolate brands taste rather funny these days. I think it's due to Cadbury's being purchased by Kraft, and their recipe uses a lot of oily ingredients to compensate for the lack of cocoa. But it's all unhealthy anyway. The Wispa Gold has this chalky, burning taste, and is nothing like it was years ago.
When you bite into a Mars bar, the chocolate no longer feels smooth and tasty. Just snaps off like a choc ice, and tastes sickly due to all the excessive sugar.
Some people may find dark chocolate too bitter. But all the other kinds of chocolate is just too sugary. Rolos and other childhood favourites just taste like earth now.