Oh that was terrible - from a film perspective - much of the backlot was destroyed. I have seen many photos of it since it happened Sunday, and so many classic sets are now just rubble. Some of the classic films and (not so classic, too) that were filmed there where the fire ravaged, and destroyed... include so many more than I can even think of right now, but here's a tiny sampling:
Back to the Future
The Sting
To Kill a Mockingbird
Gremlins
Frankenstien
Abbott & Costello Meet Frankenstien
Spiderman 2
countless TV shows
and so many more
My first job between my sophmore and junior year of HS was at Universal Hollywood - and I spent many an afternoon down on the backlot that summer, so it was sad to see so much of it engulfed in flames. The backlot dates back to the '20s, and it is the only "major" backlot remaining in So. Cal. Many, many studios use it, including Disney. Parts of all 3 POTC films were shot on the Uni lot! Hollywood's U.S. is an actual working studio, whereas Orlando's is more a glorified celebration of film through attractions - and a few soundstages for tv stuff.