The higher you specialize in each weapon will determine which are available to you. So a paladin who dumped the vast majority of his specialization points in to slashing will likely have more slashing combat styles at his disposal than one who shared points among multiple weapon skills or one who focused primarily on spell casting. Fighting classes can also specialize in shields now. In addition to increasing their ability to block attacks specializing in shield will earn you the new guard skill. Guard is not the only defensive skill.
Fighters can also protect or intercept.
Protecting a player will make a monster less likely to transfer their anger to that player when they heal another or when they cast a damaging spell on the monster. Instead they will be more likely to focus their aggression on the guarding player. Intercept is a last line of defense. It allows you to jump in front of an opponents attack, causing you to take the damage instead of another player. This might be useful for saving another player until they can be healed.