I did not understand it at all at first. It's really not very intuitive. The subject line isn't really a subject line (like with emails)...it's really just the first line of your response.
And it was annoying to have to click on every response to see their full response. I was used to forums where you just scroll down and you see everyone's full responses.
After I got the hang of it I started to see why this format is better and now I love it. I totally get the criticisms though