Hi,
My Channel Five picture quality is fine with no blocking/artifacting at all, on Freeview.

Yes, the picture occasionally goes blocky, but that's only because I live in a not-very-good-reception area for Freeview/terrestrial TV.
If anything, since the Freeview retune, I've had better signal quality and can now get more channels!
Sorry to hear that many of you have had problems since the retune. I now it may sound stupid, but have you all completely reset your Freeview boxes and/or done a complete channel search, again? Sometimes, that can cure the problem. (I appreciate the fact I'm preaching to the coverted, as the saying goes, so apologies if that sounds like I'm being condescending. I'm not, honest.

)
Pooch