We have been to Disney World 4 times in the past 3 years, each during a different session and it seems to always be busy. We are looking at going to
Disneyland for the first time after Christmas (Dec 27-30) . How bad are the crowds during these times? Thanks!
I hate to be the bearer of bad news, but probably the worst it can get.
I wish I could have given you better news, but it will be very very busy.
But don't feel alone, I will be there too on the 29th. But I have been there before, and know what to expect.
I would suggest that you make some dinner ressies as soon as possible, if you haven't already done so. Make sure to use your fastpasses to the max. Get them as fast as you are allowed. They will run out. Get them for the Holiday Haunted Mansion, Space, Indy and Splash. These all run out the fastest.
You might be warned about leaving the park and getting back in again. Even if you have already had your hand stamped and everything.
California Aventure will be less busy, so take advantage of that when it is unbearable at DL. The fast pass machines are not connected to DLs, so get more.
Enjoy what you can, especially the absolutely beautiful decorations.

I go this time of year just to see them.

You should also schedule for the fireworks as soon as you can, as they sometimes get cancelled due to winds. After the fireworks it snows along Main Street and over by the Rivers of America. Plan for the Christmas Fantasy Parade in DL and over at CA, the Main Street Electrical Parade should be running.
I hope this helps!
