Wow, I never realised how MUCH 400 sheets of paper is! This is 2.2cm thick!! Because of this, it's not ideal if you want a pad of paper to carry around. However, you can tear pages out, and this is useful.
It's a cardboard backing, so it bends; this gets a bit annoying if you're trying to write on your lap, or on an uneven surface. However, because it's so THICK it is still possible to write - it's just that the paper'll be curved.
The paper is good quality; you can write on both sides of the paper in biro, no problems about the pen showing through. However, I tried a permanent marker and, like most paper, that does show through. The paper is white (unlike some purple paper I've seen in poor quality pads!) and the lines are normal lines, with a standard red/pink margin line and four hole punches along the far left of the page.
All in all, this is a good pad of lined paper.