That's a lot of dirt and even some more serious particulate matter built up in there. Note that this is the side of the filter connected to the mask, so what you're seeing here is more or less what I've been breathing out, whereas the other side (which is similar) is the dust getting past the other two filters. Seeing how much this filter is catching makes me glad I bought the supplemental filters.
I've been having difficulty sleeping the past two days, and it caught up to me today, when I went back to bed shortly after noon and slept for about six hours. I hope this doesn't completely scramble my sleep cycle for the week.