We just went Nov 29th-Dec 7th. It was not busy. There were a few 15-20 minute waits, but we basically had 1-6 minute waits. The longest waits being Autopia, Space Mountain (but we got a FP and got on in 5 minutes) and anything in Fantasyland.
We were there the weekend of the Candlelight processional. We had tickets for Sunday night. We knew it would be crazy busy, so we went to Sea World saturday, and then stayed in CA on sunday, had our required meal at Storytellers, got our tickets to the CP, and went into DL then.
We heard DL was at capacity the next weekend though! (Dec 10th)
So the earlier in the month you can go, the better.
(A CM told us the park seemed to be at about 35,000 while we were there, so that is not bad at all!!)
The Christmas decor was beautiful!!