When you call something incomparable, you mean it is so good, so beautiful, or so striking that nothing else comes close — beyond compare. It is praise, and a little grand: incomparable beauty, an incomparable voice. You are not filling in a score sheet; you are saying comparison feels pointless. The word can also stay closer to its pieces: two things are incomparable when they are not the same kind of thing, so it is unfair or impossible to rank them. In careful talk some people even move the stress (in-COM-parable for “cannot be compared,” incom-PAR-able for “matchless”). Though actually, most speakers do not fuss over that, and the “extremely good” reading is the one you will meet in ads, reviews, and love letters. Do not say more incomparable; the word is already at the top.