The Best and The Rest

Naota has made a great post on what makes FAS, FAS as well as what makes it unique from other games out now. In summarization, FAS stands out from the rest because of:

Guns... copious amounts of guns
A Genuinely Balanced Skill System
A Unique Loadout System
Reinforcement-based Victory Conditions
Reloading that makes logical sense
The Firearms Menkey
Ludicrous amounts of other interesting mechanics

To find out more, you can view Naota's post in the FAS Forums.