Based on my own experience from last year:
Disneyland was very, very crowded. The parade ran twice at 1:30 and 3:30 (instead of 3:30 and 6:30) and the fireworks went off 20 minutes later than usual or something like that to help thin the crowds out some. The CP has two showings. I can't remember the exact times, but the second one starts around 8:00pm.
For me, it was well worth dealing with the crowds. The Candlelight Processional was absolutely beautiful and has taken it's place in the upper echelon of special Disneyland experiences. The choir starts at Small World and proceeds down Main Street holding candles before arriving at the stage in front of the Train Station facing the castle. While they go down Main Street, the lights are dimmed and the choir sings Christmas hymns.
Once they arrive at the stage, the narrator takes his or her place and tells the Christmas story with the choir performing Christmas hymns throughout the telling of the birth of Jesus Christ. There are trumpeters atop the train station who perform periodically throughout the performance. I was in tears at the end and had a very difficult time trying to thank my parents for teaching me about Jesus because of the emotions of gratitude this experience swelled in me.
A couple of notes about the CP. I think we lined up around an hour and a half before the second show(which is usually easier to see). One of our party was in a wheelchair though so I'm not sure of how early you need to line up if you don't have a wheelchair. Once Disney fills in the wheelchair viewing area, they will allow people to line up behind them.
The only way I would not recommend the CP is if you have young kids. They may have a hard time waiting for hours to see a show that's roughly 50 minutes long. But it is beautiful experience. I'll deal with the insane crowds again because I believe it's that good.