This works well for how I read slashdot - I scan down the page for interesting comments, and then open some of the summarized lower level children in a new tab and read through them. If someone posted an interesting point, it is easy for me to view all of the replies.
Admittedly, I have not used the beta much, but I have not been able to figure out how to read in my style. Say that I am reading at the +4 comment level. I have no way of discerning if a particular child comment is replying to the +4/5 parent above it, or if there are several intermediate posts. I have no way to see all of the replies to a particular post.
My experience with classic mode is that I'm reading a conversation, and I have a choice of where I want to dig in further to the conversation. My experience with beta mode is that I'm just reading a bunch of random comments with no good understanding of their relation to each other.