I looked throw the main fetures of X2 and was quite disapointed, because things which I like(and I gues many people too) are planed to be replaced. And I'm talking about geoscape.
Air combat was super cool. It was interesting stratigically and tactically . I would like to see how it's evolve, becoming more interesting with different options for different strategies. The atmosphere of X1's feels whery realistic to. In X2 there some sort illusion of control. If you have enough power you will beat UFO. It only depends of random, how many damage your fighters will receive. There is way come up with any kind of tactic. Yet again it feels awesom when you direct your planes in X1. You realy feels like commander.
Plenty of bases was also nice. As for me, the logistic was interesting. It maked atmosphere of serious organiztion as well. It also can evolves to become more interesting for player. Base planning system was interesting too. I'm sorry but my first thought when i saw ATLAS was "XCOM", but this kind of vertical construction is't best part of it.
I like clever game X1 was, but ut looks like X2 lossing best of Xenonauts.