From the films:
"Mutation: it is the key to our evolution. It has enabled us to evolve from a single-celled organism into the dominant species on the planet. This process is slow, and normally taking thousands and thousands of years. But every few hundred millennia, evolution leaps forward."
—Professor Charles Xavier, opening of X-Men
About the franchise:
"A final personal note: As a fan of the series, I want to say thank you and goodbye to everyone who gave us 19 years of X-Men superhero team-up entertainment at Fox. The franchise served as a proving ground for concepts and effects later employed by other studios to expand our understanding of what's possible in the superhero genre. From grounded gritty storytelling to ensemble team-ups, from convincing superhuman powers to spinoffs and soft retcons, from R-ratings to loving self-satire, X-Men was groundbreaking and deserves our respect for its many important accomplishments."
—Forbes film journalist Mark Hughes, at the end of his review of Dark Phoenix