5. Destroy All Humans! (2005, PlayStation 2/Xbox)
Though it may not stand out in terms of scale - hey, it's one alien! - Destroy All Humans! offers one thing other alien invasion games can't quite match: you're the alien. Playing as Furon clone Crypto-137, you take to the Earth to molest, explode and harvest the DNA of the entire hapless human race.
This blend of 1950s sci-fi kitsch and high-powered, free-form action is certainly the most amusing alien invasion on our list. When you're using your anal probe to burst the heads of happy Americans and extract their brain stems, you'll realize: being the invader is as fun as repelling the invasion.