Sequels were not rare in the 80's. We had PacMan, Ms. Pacman, Baby Pacman, Pacman Jr, Super Pacman. Galaga, Galaxian, Galaga '88. Donkey Kong, DK Jr, Mario Bros, SMB, SMB2, SMB3. The big games always get lots of sequels.
I will say that annualization is negative. In particular, in the case of COD which consumes such a large part of the market it is negative. In the past you could release a title in year Mario or whatever was not coming out and be the star of the show. Annual titles mixed with very large budgets is making it at least a little bit tougher for new ideas. But we are still seeing new games. Eventually a new style will probably push shooters down a little, like platformers and fighters in the past.








