Though mostly a 3.5 set, there are significant variances. Familiarity with Pathfinder will help understand some of these, but is not necessary. Unless otherwise stated, assume the rules a 3.5.
Ranged Combat: Enhancement and Quality bonuses (including Masterwork quality) from ammunition and bows or crossbows stack.
Death occurs at negative CON hit points, rather than at -10.
Damage is debilitating. Any successful hit has the potential to be damaging (and all criticals are). Further, at 75% HP, a character takes a -1 penalty to all d20 rolls. 50% HP, a character is considered fatigued, and takes an additional -1 penalty to all d20 rolls. At 25% HP, a character is considered exhausted, and takes an additional -1 penalty to all d20 rolls.