Sort of spoilers for campaign progression:Warning: Spoiler! (Click to show)
Once you use the arc projector on one of the crystal-like ship commanders you'll be able to research an object that will open up the mission to invade an alien base. Great mission, tons of enemies and led to the moment I thought I was about to lose my whole squad.
Really like just about every way they've trimmed and massaged this game compared to the two originals. Skills take the place of the soldiers getting increased time units by doing things like letting you shoot twice, move and still shoot with sniper rifles, or even just increased move range. I kind of still want a squad size of 7 or 8 (or at least the robot unit not counting towards your 6) but the soldiers are more powerful than in the originals. The smaller squads and ease of actions also leads to most missions taking significantly less time than they did in the originals.
My most intense moment was flushing out 3 Crysallids who then moved to within 1 square of my high level Assault. I thought he was meat, but he used his double-shot to kill one, my sniper got a lucky head shot on one that was wounded by overwatch, and then two other members of my squad finished off the 3rd.
Oh, yes the aliens will use mind control. Thankfully if you kill the alien you'll have your troop back immediately. Also really like how missions immediately end when you kill the last alien instead of you having to finish out all your moves.