The three things that matter most about your weapon as far as damage calculation is concerned are type (blunt, piercing, etc), affinity (water, fire, etc), and class (beast, undead, etc). The amount of points you have vs the amount of points the target defends against in each of these categories is going to determine how effective your attacks are, and they all matter, but some are more heavily weighted in the calculation. Type is the most weighted of the three, affinity is the second most weighted, and class is actually last. The reason why it is common to focus on class when building your weapons throughout the game is because it is by far the easiest of the three categories to continually modify (since you just use certain weapons on certain enemies consistently), and while not as weighted as the other categories, is still a very important piece. Later you will be using lots of buffs & debuffs, as well as socketing your weapons with gems that boost affinities--this is where you are going to shine in the elemental affinity category. Pull out your best weapon for whatever enemy class the boss is, socket it with gems that boost your elemental attacks on the element he is weakest against, and then use your buffs/debuffs to exacerbate the differential.