I was there at DLR yesterday, too, and the crowds were delightful for the first few hours of the day, then they picked up. When we went on Haunted Mansion Holiday, it was a short, reasonable line.
Honestly, even in the early evening/late afternoon, while we could see that Main Street had filled up with people compared to what it was in the morning, it was still not as bad as I've seen the crowds at DLR before. The crowds did not appear as bad as when I was there on 11/13 last year, for example. But the lines for specific rides will get long.
I have always maintained (when anyone asks about opening day crowds), that people will flock to the parks for the novelty of it - people want to see what is new or different from last year's Halloween stuff (or Christmas stuff), and they want to be there on the first day of the seasons. I have never changed that opinion, and that's what I always tell people. I will say that it won't be New Year's Eve-level busy, and that it will be manageable. However, I think other DIS'ers on the board sometimes tell people that the crowds will not be that bad.
So I guess that I will say it was crowded yesterday, but not nearly as crowded as I have seen the parks on my Christmas holiday trips.
I think that when the Halloween Party begins and October rolls around, it will become even more crowded.