Wow, lovely tutorial! One thing though, when I put it to the same settings as you have, the lines seem so much more blurry than yours... yours seem so crisp! Any possibility you accidentally screenshotted the wrong settings?
Here's a really bad example of the first step I did with the brush settings you have here:
I found this browsing dA so its a year later, but if you're still having this problem, its probably not just the density, but you might not have pen pressure on. If you have a tablet like Bamboo, that has pen pressure, but some don't, and you can't use it with a mouse owo
its all to do with the tablet. i have the intuos four and it has a very different set of behavior even to the new wacom bamboos i have tried. this feel so much better as it has a more lucid response to it. more communication between it and the pc