Making their original appearance in a self-titled 1982's Marvel Graphic Novel, the New Mutants were created by writer Chris Claremont and artist Bob McLeod and served as the first major expansion to Professor Charles Xavier's School for Gifted Youngsters since the All-New X-Men years before. Over their original 100 issue run (which also featured the artistic hand of creators from Bill Sienkiewicz to Rob Liefeld), the core team including Cannonball, Dani Moonstar and Magma amongst others confronted both growing up as mutants and facing down supervillains for the first time. The new series (which will replace the soon-to-wrap "Young X-Men"), promises to feature the majority of the original book's core cast after graduation in a much more dangerous world for mutantkind than they once faced.
Another blogger recently wrote about the confusing changes in Moonstar's powers. This is the key problem with Moonstar that I mentioned before.
I'm not sure how well the new NEW MUTANTS book will work, either. The problem is that Marvel has created too many X-teams: the X-Men, X-Factor, Excalibur, X-Force, Generation X, the New X-Men, the Young X-Men, et al. There are so many overlapping teams that few of them have a clear raison d'être. Since the eldest X-Men never grow old or leave, the newer mutants have nowhere to go except to irrelevant side teams.
For more on the subject, see Comic Books Featuring Indians.