The Covenant and HGHs fight so differently though.
The Covenant are more zone oriented, protect large spheres and they usually go about the business of killing you within their specific zones. The Brutes and Elites will hunt you down, but you usually have to really agitate them in order for that to happen.
The HGHs seem less zone oriented and much more eager to counterattack and hunt you down, using the environmental factors to their advantage. (i.e. shifting their bodies behind cover,switching from cover to cover, shooting explosive barrels)
In some ways, the behaviour of KZ2's HGHs reminds me a bit of the Elite behaviours in H2, (Mind you the typical Helghast grunt is nowhere near as agile or strong as an Elite, but they can catch you off guard and surprise you from behind.)
but I'd say KZ2's AI is more reminiscent of F.E.A.R. and Half Life.