This is madness!
The first thing I noticed was the bizaare creatures I could hunt- although the whole hunting thing is a lie since they know you're there and move to attack even when you're cloaked far far away from them. Somewhat disappointing and I wonder why they don't attack each other when I have a miniature legion of reptiles and wild beasts trailing me. So going past that we progress through the level and fight some Aliens. Oh yes this feels great as I chop them to bits with my blades or try to gun them down with my wrist gun. Of course I've been here before but it was all good. After this short skirmish I ended up fighting more all knowing wildlife in the form of gigantic worms who pop up beside me and give me a cheap whack over the head. What's worse is that I never know if they're dead- they just keep popping up.
I'll say this about the rest of the story and progression. It ends very quickly right when you're getting into the game. They give you new things to mess with and take it all away immediately there after. Now I'm sure being a Predalien in the Alien campaign would be fun, but the promise of the campaign being short disuades me from trying it for more than an hour.
At the end of the day the Expansion is not giving you anything more than what AvP2 gave. It's very much not worth the buy unless you can ignorantly ignore the shortcomings. Another disappointment was how fragile they set out to make the Predator in Multiplayer. The cloaks just don't work the way they should. I think a bit more 'expansion' to the Expansion is necessary though it will never come. Avoid the expansion, but continue to love AvP2.