How is it the worst?
A run-of-the-mill war game (Medal of Honor being no better) with poor cinematics and gameplay. It's incredibly stereotypical in practically every way. The stories are rather bland, and you would rather skip them to get to the action.
I played the first and second long ago and they were playable to the end, but they were not impressive.
Everything past that has gone further downhill.
This is, of course, just my taste in video game shooters.