Alright, so MEC troopers are fucking insane. I keep losing troopers to wounds and ill-timed enhancements, so one mission I had nothing but a squaddie MEC and 3 rookies. I literally sent him alone to kill 4 sectoids, in full confidence that he would win. Against thin men his health was quickly depleted, but still... 6 damage minigun, an ability that takes away overwatch aim penalties, and the ability to kill enemies by Kool-aid manning through walls. What's not to love?
You can't get enhancements and laser rifles for the first terror mission, unless you perform an autoposy to speed up beam weapons. Autopsies also unlock new genetic upgrades. All of this means that South America might actually be competitive with Asia as a starting position now. My start in II is definitely going to use MECs, as they make Crysallids trivial (although its very tough to have two of them by the terror mission). In case you're wondering, the balancing factor on MECs is that they can't take cover...ever. Using them requires using concealment, breaking LOS, and BLODDY MINDED MELEE RAGE.
The new AI is less skilled but more unpredictable. A one health floater managed to take out the medic by leaping into concealment behind the squad, and then jumping over the wall to one-shot her. Floaters also now use their ability to gain the height advantage on shooting, even if there is no cover around. On the flip side, they've made some pretty stupid moves that I've seen.
The whole feel of the game has changed for me. Between the time-based meld collection, the aliens attacking from all directions, and the MEC-troopers ignoring cover, the game feels much more mobile and fast paced. The first mission that hints at EXALT is fucking brutal; the level was set up so that thin man could always hit you from roofs, and the alien drops had 2 3 alien waves, and then 2 1 alien waves. I didn't check to see if they kept coming past that. All in all I killed 13 aliens, 12 of them thin men... before the first terror mission. While escorting a VIP. I'm actually going to say that that mission + that level is unfair, although I had no casualties. The new levels as a whole are difficult, but none of them so far are cover-less "murder streets", which is nice. I've only played 2 levels that I recognized.