Nice to meet you Torontones.
"Alien" movies are always welcomed by me, until I see and throw out the really really bad ones. I have no problem watching a B-movie where you can see rubber masks and cardboard sets, but, a rotton story and can ruin even the biggest blockbuster film.
I can't pin down just one "invasion by unearthly beings" movie, so I'll mention a few of my favorites.
Godzilla: Final Wars (2004) Lot's of giant creatures fighting with the King of the Monsters.
Zontar: The Thing From Venus (1968) Great remake of It Conquered the World (1956). I love these movies where ONE alien takes on our planet.
They Live (1988) A John Carpenter masterpiece!
Daleks-Invasion Earth 2150 A.D. (1966) Peter Cushing made a great Dr Who. Sequel to Dr Who and the Daleks (1965).