Sound.  Sounds in a warfare game are paramount for me.  They can make or break the whole experience.  Ghost Recon Advanced Warfighter 1 for the PC, I believe, had some of the best sound effects I’ve ever heard.  Bad Company 1 rivaled GRAW with their sounds.  A lot of developers don’t realize that when you shoot a firearm it creates an echo.  Also, light travels faster than sound, so when I see an explosion a several hundred yards away, I should see it and then hear the sound afterwords.

Those are my thoughts and I really hope that Bad Company 2, which is supposed to be released on the PC unlike BC1, is a longer, nicer looking iteration of the first version.  Check out the trailer below.  FYI it’s just FMV and no in game footage.