Yes and no. Yes, it’s more crowded, but it’s magical, and so worth it. If you go for the Christmas experience, you won’t be disappointed. If you are only going to ride the rides, you might be.
At Christmastime - the best things to do are:
Haunted Mansion - Nightmare Before Christmas
It’s a Small World Holiday
The Christmas Parade
Fireworks and snow on Main Street
Just being there to soak up the lights and the magic.
Yes, it will be crowded, but if you slow your pace and go for the above reasons, you’ll get it all in and it will be a magical experience. The lights and decorations are absolutely amazing and it’s the best place to be at Christmastime, IMO.