I have always been taught, and have used, the word "чем" when making comparisons (or the genitive case sometimes). However, I have recently encountered the word "нежели" several times in books, used just like "чем". For example:
"Этот мир оказался притягательнее, нежели тот, в котором мы к тому времени прожили..."
Is this rather bookish/formal? Should I attempt to incorporate it into my speech, or will it sound strange in most situations? Does it have subtleties that differentiate it from "чем"?