Isla Mujeres is a beautiful, charming place to visit any time of year.  Visiting in the latter part of October one can enjoy the peacefulness during the low season with fewer tourists.  It is easy to make last minute reservations for tours, including wonderful snorkel trips.  One needs to be aware, though, that the changeable weather means planning such trips way ahead of time may not be the best idea.  Also, since this is the low season, many of the restaurants listed by TA as the Most Popular are closed until after Dias de Muertos (November 1st).  Several of the restaurants that are open offer discounts - so worth asking.  Visit the Turtle Farm (you may be lucky if you are here when they are releasing the babies to the sea!) which is interesting for all ages.