HAH! You're funny.
The first half is always the hardest and takes the longest to do. I have to create the new environments, design new characters, route out the flow of the chapter, realize that it's stupid and do 40% of it over, write the first several scenes to get the ball rolling, have the beta testers ruin my hopes and dreams, and finally pose! As I get closer to ending the game (Only two chapters left), it gets even more difficult as I work to ensure each branch/path has sufficient content.
Once I get to the halfway point, everything gets MUCH faster. It's pure writing and posing (with the beta testers still ruining my day throughout).
As of right now, overall, I'd put the update at about 25% to 30% done. This is one of the downsides (and upsides!) of the size of my updates. They are massive, as you know, and with the exception of the beta testing, I do it entirely by myself.
Edit: I just want to say, my intention is for BTW to be in a finished state by the holidays this year. Once that's done, I'll immediately start working on "0.5", which will be a prequel to BTW, telling the story of Euchora's past. It'll take place during the final days of the conflict between Alora and Alorine, and give us some history about the main character(s) of BTW.