Josh Groban, Andrea Bocelli and Sarah Brightman are not really my "cup of tea", but I totally admire and respect them. I have heard a couple of Groban songs that I really like.
The Chilli Peppers are an acquired taste. If you are not into a fusion of pop, rock, funk, punk, and hip hop, you probably won't like them. Some of the lyrics from their earlier days left a lot to be desired. I was kind of indifferent to them for many years, until their last three albums when they started using more melodic sounds, textured guitars/bass, and these incredible, multi-layered vocals. I've never seen a band mature as much as these guys. John Frusciante is one of the most innovative and unique guitar players of all-time IMHO. Same goes for Flea on the bass.
But that's just me. I'm into a wide range of artists, in a wide range of genres (from classical, to jazz, to oldies, to classic rock, to prog rock, to R&B, to funk, to disco, to pop, to new wave, to metal, to alt. rock).