Traditionally, week two of NaNoWriMo is where it all goes downhill. Plots fail, word counts flounder, characters flail uselessly. Week Two is where it gets "interesting".
Wash: This landing is gonna get pretty interesting.
Mal: Define "interesting"
Wash: [deadpan] Oh God, oh God, we're all gonna die?
The same thing often happens on a larger scale with your second NaNoWriMo novel. I made the 50k, but the story was depressing, and I'm never writing chick lit again. My third NaNo was firmly back in the sci-fi camp, and it was an awesome ride, despite starting a week late. I had fun with the fourth one too, which leaned slightly towards fantasy. This is my fifth year doing NaNo and I started week two ahead of my personal schedule with a comfortable cushion of words between me and oblivion.
River Tam: Put a bullet to me. Bullet in the brain pan. Squish.
Monday night my bad guy barged into a scene where he wasn't supposed to be, and seriously advanced the plot. My sidekick has been helping everyone get established, and it's about time for a new character to step in. Things are going surprisingly well and I should hit 30k by the weekend.