If you vault over him too many times, he'll gain the skill 'vault-breaker' and start blocking your approach. The best way to hit him is to vault over his shield and attack him from behind. Let's say you're fighting a shield-toting defender-class captain. This punishes spammy attacks and puts you on a timer, which breathes quite a bit of life into fights. Captains will actually learn your strategies and adopt counters to them mid-fight.

More impressive is the new 'adapt' system.