Tickets are generally too expensive. Compared to other major/major-ish championships that race at the same tracks (take MotoGP and FIA WEC as examples), F1 tickets for the same kind of entrance/grandstand seating are about 5-10 times more expensive. Take Silverstone as an example of event where all three championships race:
F1 weekend tickets at Silverstone - from ?175 to ?460
MotoGP weekend tickets at Silverstone - from ?70 to ?90
FIA WEC weekend tickets at Silverstone - ?40
With this, Monza under threat, teams in financial trouble left and right, Horner whinging and throwing about 40 tons of toys per second out of his pram, Bernie + CVC sucking all the life out of the sport and the new regulations being a good idea implemented incredibly badly... I think I'm just about done with F1. WEC, Indycar, Nascar, BTCC, MotoGP and other various series and one-off races will serve me just fine through 2015.