The Pilgrims of Rayne (Pendragon) by D. J. MacHale
I like to think an author knows his own work. In the preface, MacHale advises the reader twice to start at book one in the series (and presumably read two through seven too) before reading book eight. Then he has the main character say the same thing again on page 4.
I stopped reading at the third warning to read the other books in the series. I am going to take MacHale's word for it - that #8 doesn't stand alone and vote NAY just for that reason.