Yes, December 21st marked the start of a new baktun, which is a period of time lasting 400 years. I'm not sure the term cycle though is really appropriate here however since cycle implies a cyclical view of time, which the Long Count was not. The Long Count (not the actual name, the real name is unknown) was used to measure time for historical purposes rather than functioning as a ritual calendar like the Tzolk'in or a civic calendar like the Haab, though end dates for katuns and baktuns would still be celebrated. In any case, there are also time periods much longer than baktuns. The piktun is the next largest period of time, being 20 baktuns, or roughly 8,000 years. However people aren't going to start rambling about how the end of the current piktun signifies the end of the world because this piktun ends on October 13th, 4772, and shouting about how the end of days is coming in just under 3,000 years isn't sensationalist for people it seems.