... It is stand-alone though so if you are thinking of buying XCOM: EU just hold off and buy the expansion "Enemy Within" instead.
Not quite sure where you got that. From the long trusted UFOPaedia, "The PC will be sold as traditional DLC through Steam but the console owners will have to buy the Commander's Edition, consisting of Enemy Unknown, plus the Elite Soldier Pack, Slingshot and Enemy Within DLCs."
I'm pretty sure it's not standalone.
In any case, I liked the game and I think I'm going to get the expansion. Slingshot was a bit of a letdown, but this one looks pretty good. What I'm really hoping for is action flag modability. Chryssalids feel a bit underpowered to me compared to the original. I want to give them a third so they can jog in from out of sight, kill someone, and slink back into an alley. I almost feel bad blasting them in the face because I feel like they should run away.
On a related note, one of the few things I liked about TFTD was the Tentaculats. So I think Chryssalids should be able to jump up and hit flying soldiers for reduced damage, or the expansion should include flying mech chryssalids with rockets for legs, armor ignoring plasma mandibles, and eggs that hatch on zombie death.That would at least balance the lack of retreat.
Overall good game, but it makes me miss the days of games like Dawn of War where everything was possible with a value change and, on heavy jobs, some LUA scripting. I would bring back some double digit stats and replace flags with TU'S. Modability is the point to sell if you want to please the masses, but hook niche gamers who still care about stuff like OXC. I really hope Firaxis turns that around, because they promised modding, and all I've seen is editing.
