I just got unlucky enough the other day that a UFO found my base and attacked. I stationed my guys around the nearest entry points, and waited. One of my guys got vaporized from out of nowhere from two soon-to-be-roasted aliens, but after that I waited for ~10 turns and didn't see anyone. I got impatient and marched my guys outside where they found two aliens just dawdling. One was right next to the main entrance, and the other was behind the radar tower. I killed the one at the entrance the second I saw him (pistols are a lot more powerful than they look) and the second guy was just standing immobile under the radar tower as I worked my way towards him.
Is there something wrong with the alien AI that doesn't make them all storm the base? Am I just not patient enough and need to let them take some time to come down? I should also note that defending is especially tedious as reaction fire still does not work properly for me
Also, a sneak preview of my slowly growing feature request list:
auto turret defense guns for the base would be really nice. Is it just a matter of there is no art content? or does somebody think they'd be unbalanced?