I don't think we know just yet what crowds will be like. Here is how I am envisioning things:
This year is a whole different ballgame because of World of Color coming to DCA, and the impact it will have on that park as well as on DL. Since it appears that the Trick or Treat Party may be moving from DCA over to DL, that will affect DL's hours. The TOTP always runs on Halloween and, I think, the night before it too.
However, if the TOTP is going to be held in DL instead of DCA, then that means they would have to close DL hours early on all the nights of the TOTP, meaning that - in my opinion - DL will probably be jam packed with people earlier in the daytime on both Halloween and the day before it. People who are not going to the TOTP will want to get as much activity in at DL before the park closes for the TOTP. People who don't see any traces of Halloween stuff at DCA will wander over to DL to see what's there. At least that's the scenario I am picturing.
So I believe it will be a madhouse this year. Hopefully I am very wrong! It's only a guess. Even if it is a madhouse, you can still have fun and work around certain things to have a great time...but I would fully expect heavy crowds this year, especially over Halloween weekend. I would probably still go anyway, but I would just be mentally prepared!!
Last year in December, we went on the same weekend we had gone for the previous 2 years, and the crowds were substantially heavier all day long. I was not prepared for that because I was expecting the same sort of crowds we had encountered in 2007 and 2008. October was also more crowded than it had been in 2008, so I think this year will only mean more people. But it is manageable with the right planning and preparation!!