A huge disappointment after Aliens Versus Predator 2.
Like the base game there's three campaigns, one for the humans, aliens, and predators. The human campaign actually follows a Corporate Mercenary this time around while the Alien campaign follows a Predalien instead of the standard run of the mill Aliens we see most of the time. The campaigns are all actually prequels to the original AvP 2 story with the Predator and Predalien campaigns actually beginning five hundred years before the AvP 2 story. Essentially the campaigns focus on how "the incident" from AvP 2 started.
The campaigns themselves are poorly designed and focus more on simply being ridiculously difficult for the sake of being ridiculously difficult. You've got infinite spawning aliens everywhere, and an overuse of Praetorians and Predaliens which makes playing as the Corporate (who is actually weaker than a marine) a genuinely frustrating experience.
There actually aren't any improvements from a gameplay perspective; the Marine and Predator get a couple of new toys but nothing really worth mentioning as they have a minimal presence in the actual game.
Primal Hunt is just not very good. There's not much in the way of useful new content, and the campaigns are tedious and occasionally frustrating slogs through waves of overpowered enemies. If Fox wanted an expansion they really should have had Monolith design it.
+ The campaign storylines didn't have continuity errors with the original AvP 2 campaigns at least
- Difficult for the sake of being difficult
- New content isn't worth the price of admission