YouTube suggested the latest vid (attacking a large UFO). You could certainly see a difference there. The aliens seemed to be "sniping" more, and rushing out of the ufo like a tsunami (in a regular game, you usually would need to wait for around turn 30 or so until every alien is out of the ufo). This is also a downside. As you could see, there might be even 4-5 aliens clustered together, easily killed with a single grenade. You may need to make the rushing out less aggressive and/or ensure that they don't stick around as easily killable clusters (like your soliders were). One criteria might be that they might prefer to move so that they could have enough TUs to end up in a covered spot and at the very least not next to other aliens.
As an improvement of your own battlescape tactics, you should always use smoke grenades if you don't have other cover and especially if you have many people in the same place (= otherwise an alien grenade magnet). The aliens can't get visibility on you while you are in a sufficiently thick smoke. So in that mission, you might have avoided almost all casualties by using a sufficient smoke cover.
Because the aliens don't have smoke grenades, they cannot protect themselves in this manner. But you should certainly try to avoid the aliens imitating the "basic" battlescape tactics where you deploy all your troops in the same place.
A very nasty alien tactic might be throwing grenades at smoke-covering areas, in the hopes that they would hit or wound someone. But this might be too brutal.
