I feel like the enemies in Xenonauts aren't aggressive enough in comparison to the old XCOM i still play from time to time thanks to the OpenXCOM+Extended mod , the maps are often huge and getting to each of them is sometime annoying .
Especially when the ones hiding inside of the downed ufo aren't getting out (and unlike old XCOM you can't make your own "entrance" in a downed UFO) they sometime open the main door but still stay in for some reason, very annoying hiding behaviour that contradict a lot what the lore is telling you when you make the researches on them (they're all mostly mindless drones controlled by a few brainy leaders and all of them are without any sense of self-preservation, so they should never hide according to that)
I have read that an earlier version of Xenonaut had the AI very aggressive but they changed that for some reason, sadly the GOG version is only the latest one, i would have loved to play with an AI that comes to you and the community edition just keep the same default AI as the base game.
There's a couple of mods ( "X-Division" and "XNT into the darkness" ) that have supposedly a more aggressive AI, but they change and add way too much to the game for my own tastes to give a try.
Still Xenonaut despite lots of good idea (better quality of life interface, presence of some cops/soldiers in missions instead of only civilians, etc...) and obviously very nicely polished graphics still does not have for me the magic of the old XCOM , and i surprised myself to go back to it (thanks to openxcom/extended+ mod for the improvements over it) and have again lots of fun wasting my squaddies being mind controlled by aliens and shooting their blaster launchers at my own troops