Something incomparable cannot be compared to anything else. Incomparable is usually a compliment for people and achievements that are extraordinary.
When we compare things, we notice similarities and differences between them. However, when something is incomparable, comparison is impossible because what you're talking about is so amazing. You might say that the paintings of Picasso are incomparable masterpieces or that the Grand Canyon is an incomparable sight. People do tend to exaggerate, but this word should be reserved for the truly outstanding.