XCOM: Enemy Unknown

Not a problem at all, and the further you go, the easier the game becomes. The basis of victory is plasma weapons, especially sniper rifles (2 snipers in a squad are very desirable), then the enemies generally die in batches, no matter how strong they are. At the initial stage, the main thing is to solve the problem with engineers; their shortage can VERY slow down development. And satellites must be launched en masse at the first opportunity. A plasma cannon is also ideal for airplanes, then they will shoot down anything. On this difficulty, enemies with plasma weapons appear quite early, so you can research them a little later than laser weapons, which are not worth wasting time on.