Topic: Terrain that alters masking/detection value
I would like to see some kind of terrain (swamps with heavy gas, forests, fault lines with EM radiation etc) that reduce the visiblity (and possibly detection) of the units inside. With a well fitted scanner being able to see most of the island, and gate watchers (->proximity sensors) monitoring the entrances it is possibly a little too easy to see almost the entire island.
Perhaps some patches where movement could be allowed undetected, or areas to run into that then give you a couple of options to run out of would add some more spatial and tactical depth to the game.