Not much, I reckon. This might help - Anthony Davis, developer, on the game (starts off with mentioning the 'Hulk' Alien):
The little guy next to the Alien is for scale genius. This was a concept piece.
The Xenomorphs according to canon absorb some dna traits from host creatures. The two in question here were the behemoth, taken from a very large herbivore, and the second was something were calling a stalker, essentially an Alien that can cloak like a chameleon, taken from a chameleon type creature host. There were also Queens, scouts, soldiers, spitters, and more - including black and red variants for those who know the material.
The game was most certainly NOT a grind fest. Experience was awarded for completing objectives and stealth was greatly encouraged.
Basic gameplay was your party was composed of 3 to 4 members. Party members could be from 1 of 4 different professions, marine, agent, engineer, and ugh...I forget the 4th at the moment .
In addition to stealth, party members could place traps for Aliens, such as turrets, mines, door bombs, and more. Doors could also be welded or cut to slow down Alien movement and create bottlenecks.
There was research, crafting, base defense and much more in the game and working.
[in response to criticism of the two new Aliens above]
First of all, I only addressed the two pictures. I didn't talk at all about the story and what was going on at the location for the game.
Second, real life (edit) players who would have played Aliens:RPG more than likely would have known what an Alien is, probably a queen, scout, and even soldier too, while characters in the game would be ignorant of them as a whole, until they meet them, you cannot expect players to selectively 'forget' or ignore the Aliens movies and the other video games. If you are making the game we are making where there are moments of horror, you have to give them something new.
Third, the cloaking alien wasn't so much a visual cloaker, as just an alien that was difficult to pick up on the motion tracker. All of the aliens were hard to spot when they are hidden in the alien creep.
Fourth, these two new creatures were used sparingly.
Alien still had something like 20 months left.
As far as our end goes? Sure mistakes were made, the Onyx engine was being built from the ground up and we were integrating a LOT of new technology. http://rpgcodex.net/phpBB/viewtopic.php?p=817006#817006