The reviews do place the JVC into a new league. The only negatives I've seen posted (which may not be negatives, depending on your point of view) are whiter corners (for a few), lack of a color management system, and no access to the hidden menus used for color/greyscale (the latter I'm not so sure about; this was talked about prior to the release).
Supposedly, the pre-buy was a good deal. From all accounts, the JVC would be much better than the Panny. You'd have to upgrade to Blu-ray, HD-DVD, then!