I agree with giladn. The production value is especially striking. When I first saw "Heroes," I thought, "How can a TV series with a cast of mostly little known actors be so polished and beautiful?" Even if you don't love the show, you can still appreciate how perfect it looks.
In any case, I do like the premise that average people can be heroes. I also like the suspense, as you gradually learn about the characters and the world in which they live.