I would say KISS were a real rock band in the 70s. I like their first 6 albums or so, it's good pop-rock. "KISS Alive!" is a classic live album. They started to get a very young audience because of their make-up. When I was in 4th grade, they were the biggest thing ever. They started to get silly, (sillier?) starring in stupid movies and putting out concept albums. By the time the 80s came, they were largely forgotten, and 2 original members were out. They dropped the make-up and started to play the pop metal that was popular at the time.
Some time in the 90s they decided to get the original members back and tour in full make-up and costume. This gave them an additional boost in popularity, and they've been riding this nostalgia wave since. They replaced the same 2 members with new guys in make-up, which is why they look youngish. At this point, I can't see them as more than a nostalgia act.