Call of Duty is an awesome series. I've been playing since the first game, and I can tell you right now that the alterations made for the consoles' sake haven't detracted from the gameplay at all until MW2. CoD1, 2 and 4 are pure gold.
As for THIS game:
I reiterate that the Marines shouldn't be able to counter Alien attacks at the very least. The Predator has its own ranged weapons, but the Alien only has its claws, tail and inner jaw, so being able to counter it at the only distance it's effective at is just plain dumb in terms of multiplayer. At least one consolation (hah!) is that standard heavy attacks can never, ever be blocked and have good distance.
It makes a bit more sense for Predators to have Marine-blockable attacks, but I still don't like it, especially since in MP they start with no ranged weapons.
As for the inclusion of trophy, execution and stealth kills: I welcome the addition. Nothing forces you to use them, and they look like a fun alternative to spamming the attack keys.