I liked WriteRoom 2 because of the flexibility it afforded me in customizing my writing environment - it's about allowing me to focus on writing and not minutiae, right? WriteRoom 3 takes a departure, which has caused me to spend around 20 minutes just trying to get the window how I want it - full screen every time I open WriteRoom, the page is centered (I don't like text scrolling off the edge of my monitor, it's distracting. However, I can't adjust the bottom margin in 3), and a entire black background gives me a headache after awhile. After one spends an hour of customizing, and wasting valuable writing time, it almost works like its predecessor. Until you close it and open it again.
Theming isn't as cut-and-dry - I didn't see a Theme editor, so I opened a theme in the text editor (thinking it might be XML-based) and was greeted with gibberish.
Since it was an inexpensive upgrade, the value wasn't bad, and so far it hasn't crashed on me.
Sorry for the snarky commentary, I'm just frustrated - which I know is a poor excuse. I just don't like my time being wasted.