Firaxis' reboot of XCOM, Enemy Unknown, is one of the most logically sound alien invasion games you'll ever play. It accepts that if extraterrestrials were to invade the earth, it wouldn't be a single soldier in a suit of armor that fights them off by blasting his way through their defenses.
Satisfying; difficult tactical battles; The lengthy campaign and robust multiplayer; Incredibly deep customization
Camera and control problems; Random difficulty spikes; Watching your loved ones die to incredibly bad luck