From what I remember it was to align much closer to the original X-Com/UFO Defense game(s) than the recent re-imaginings are.
It was, and in truth i still play OpenXcom (which is a fixed modern OS working version of the original game) when i want that Xcom vibe. The new games have really caught peoples attention, but i never liked them as much as the originals much broader gameplay design.
Xenonauts is ok, but still not as good as the original game. The biggest (game-stopping even) issue i had was the way it could not handle trajectory of your shot in real 3D. For example you could climb into an elevated position for the tactical high ground, but if a small fence or object was in the line of sight your shot would always hit it, no matter your hight advantage.
There were other aspects of the game-play that eventually pushed me back to OpenXcom, but that was the killer blow. It was the 'best' of the new versions of Xcom, in part as it tried to keep most of the originals content, but technically it did not hit the highs of the original.