In the original X-Com, you started the tactical missions with virtually no vision on the map. This seems to be somewhat unrealistic... You would have at bare minimum done a visual scan of the landing zone (if not the entire mission area) immediately prior to landing, and more likely than not would also have more advanced scanning systems (radar, infrared, magic alien technology) which would give you increasing amounts of info based on your tech level (starting from ow many aliens there are on the map, going on to what kinds/races of aliens they are, all the way up to what kind of equipment they are carrying...)
Naturally, the aliens would have technology that would allow them to obscure themselves to an extent (for example, an appropriately shielded ship would conceal the number and type of aliens in it), but it would require a lot of effort, for example, to totally conceal a big alien tank with a massive weapons system waiting right outside your transport's door to waste you when you walk out. Also, aliens would be forced to choose where and when to deploy this cloaking/sensor shielding tech and wouldn't be able to necessarily deploy it to every mission.
Thus it would be a race for the humans to improve their sensor systems and the aliens to assign more resources to their cloaking systems (as opposed to heavier weapons, more missions, etc.). This would be a decision the AI would have to make for the aliens as the humans developed more advanced sensor tech and deployed it.
Yes, the original X-Com had motion detectors or similar, but my point is that even today we have better sensor tech than that and this is sci-fi! Other major point is that in most cases, landing completely blind is unrealistic and makes the game unnecessarily difficult. The landing craft should at least have basic visual scanning of the landing zone if not the entire battlefield.