Seems to me that every army has it's own MacGuffin.
It's own specific niche talent/equipment/ability that sets it apart from other armies.
The Tau have markerlights and jetpacks. The Space Wolves have the four HQ and Grey Hunters options. Blood Angels have Death Company.
Those are the only armies I am familiar with.
What are the MacGuffins for the rest of the armies?
Are the MacGuffins balanced?