the filtering of web sites is based on a CONTRACT (signed 17. April 2009) between the government and Internet providers. Until now there is no law at all that legalizes, in a democartic way, the whole action. The blacklists of web sites to filter is produced daily from the BKA (Bundeskriminalamt, about an equivalent to the FBI in the US) and delivered to the ISPs. This list, as well as the reasons why a web site is blocked, are secret and in no way controlled by a) the public or b) a judge. A surfer that is on the way to a (maybe) child porn site will end up on a site with a STOP sign and explanationary text. Not stated (but guessed from many) is, that the IP of this surfer will be recorded and delivered to the BKA, to investigate further.
So, from now on the door is wide open for content blocking of whatever. And since even the try to surf to a web site that may contain child porn is illegal, there is no legal way to check, which sites a blocked. At least, not from within the jurisdiction of Germany.
I think, all these un-democratic points qualify Germany from now on to be named as being on the same level of censorship as China and other government terror states.