In terms of how they shape & form the decade for me in terms of my own experiences both with the films and through the films themselves, in terms of my own life at the time of seeing them at the time, it goes a bit like this....
1) E.T.
2) Superman II
3) The Breakfast Club
4) The Empire Strikes Back
5) Some Kind of Wonderful
6) Back to the Future
7) Tron
8) Starman
9) Biggles : Adventures in Time
10) Gremlins
I feel I should now add the list from a 'generalist' decade point of view, at large, in terms of 'screaming 80's' as the thread says....
1) Ghostbusters - The defining 80's ensemble comedy
2) Wall Street - It is the 80's attitude
3) St Elmo's Fire - The Brat Pack's defining film
4) The Breakfast Club - John Hughes (the decade's director's tour de force)
5) Rambo : First Blood : Part II (The very definition of 80's action OTT)
6) Back to the Future - Spielberg's vision of support to Zemmekis & Gale's 80's sci-fi comedy gold
7) Commando - Arnie's response to said OTT 80's action
8) Die Hard - Best Action flick of the 80's and template to this day of 'one man verses enemy X in a confined space' films
9) The Thing - Practical SFX Magic & Carpenter's genius
10) Working Girl - included as it shows how feminism was seen in a horrific decade for the lack of understanding (see Wall Street for that attitude) and thankfully shows how far we've come, but more to do.