Seems to me that the people working behind the scenes are attempting to give these SB Nation sites more of a real "sports website" feel, ala Cnnsi.com, and less of a "blog" feel. That's my initial reaction.
Personally, I liked the "blog" feel. It was simple and easy to use. This new site seems too flashy and it definitely takes away from the fan-contributing aspects of the old site. The Fan Posts and Fan Shots have been pushed further down the page and have been designed to be easily overlooked as compared to the "main" stories.
Also, this isn't a "sports website" in the same way as a professional sports journalism site (Cnnsi, ESPN, Yahoo Sports)*. None of the main stories here are broken first by reporters from CelticsBlog. These are recycled stories brought here to spark discussion amongst the fan base (which is what I love). So, why make it look like a professional site when it's not?
In the end, these are blogs and fan forums, not ESPN. I think they should have stuck with the old format.
p.s. I'm also not a fan of change (in many instances).
*I understand that many of those "real" sites have devoted more and more space to personal opinions and conjecture, but they do still employ some journalists who break factual stories.