Incredible growth. When I started (1995), South Carolina had 2 courses, and 3 tournaments a year. If I wanted to play more tournaments, I had to be willing to drive 200 miles. Now there are about 60 courses or more, and the tournament schedule is crowded and starting to overlap.
As for discs, the selection's vastly greater, and the new discs have extended distance. But the big change is that I began in the error of DX-only, when you had to constantly replace discs as their flight characteristics changed.
Oh, and all the stuff everyone else has mentioned. For years no one knew what I meant when I said "disc golf"; now I'm amazed at the recognition. There were probably longer courses somewhere, but I rarely saw a hole over 500'.
Ratings and the proliferation of divisions.
Internet presence, with discussions and course directories.
This site.