They're all the same general concept... just different characters. Guy ends up somewhere, reluctantly becomes a hero and saves the area from the bad guys by killing everything that moves.

I enjoyed the first couple games as the mechanics evolved, but after awhile they started feeling kinda stale. (at least in my opinion.)

Sure. But no.

It is an FPS. Here is a setting, here is some gear N shit, now go fight!

First was the best. Downhill from there. Just my opinion, really. The follow ups just used the name and not the premise.

It's supposed to be an anthology series so they'll probably do one game a season