Regarding difficulty, I agree, the game looks great and has teriffic potential, but in some cases I feel like the aliens are cheating or are one turn ahead of me, so it's tough, mostly in the begining.
The hardest missions in my case were the Japanese alien hideout - 2-3 of my men died in the first 4 turns - the military base and the one with the office building.
I want to stress the fact that in almost all missions, most civilians get killed and the player doesn't have much to do preventing that. In some missions up to 4 civilians get killed from the first turn, somewhere on the other side of the map (see the african crash site map) and I think it's frustrating, because the objective is "protect civilians". Maybe the civilians should run towards the PHALANX dropship for cover instead of walking like idiots into the crossfire.
I would like to suggest a training map/scenario, with alien dummies, or something like that, where the player can test weapons, tactics and game mechanics, and where the soldiers can't die for real.