If you know of the Haka at all, it's probably from seeing a pre-game Haka by rugby players. While those can be impressive, this video shows the power of a real Haka.

This video shows the soldiers of 2/1 RNZIR Battalion performing their Unit haka, powerfully acknowledging the lives and feats of their fallen comrades as they come onto the Unit's parade ground. It is also an emotive farewell for they will leave via the waharoa (the carved entrance way) for the very last time.