I believe that the companies that put out FPS learned from the WW2-era of modern FPS. When the modern combat-era gets good and moldy they'll jump over to WW2. In truth, what they should do is put out a mix--sci fi shooter, modern combat shooter, period shooter. There's nothing wrong with the abundance of FPS, every genre puts out multiple games with the same general mechanics a year, the thing is when you put several of the games of different franchises/series within a franchise side by side and they come off as 99% similar.
I say mix it up and don't follow a cycle. I remember telling Outrun that FPS would've done pretty good press-wise during the 4th and 5th generation since all EA or Activision would've had to do when it came to getting a new game out is release some screenshots in a magazine, do a few interviews, and make everyone wait. Now you have to do a bunch of screens, a bunch of print and video interviews, Q&A, and several videos...then clean up whatever was wrong with the game with patches.
...you're gonna have to patch your game. Back then it just released and that was it. "What? There's an invisible wall glitch on mission 5? Can you still play? Can you go around it? You can? Well deal with it."