They are only legal if the reviewer attaches proof of all claims made in the review and the interest of the reviewer of publishing the negative review outweighs the interest of the reviewee of not having it published.
Which is the courts way of saying "it is illegal when we see it, we just leave some nominal loophole noone can fulfil so we don't go against the letter of the law". All of this is just a lot of court cases influenced by some elaborate schemes to pick the right court (LG Hamburg preferably). But unfortunately those stand as long there isn't an explicit law changing the situation. Which won't happen, because the exact same laws and especially judgements defend corrupt politicians against journalists.
Also, any kind of free-speech movement is a no-go in Germany because "buhuh, but then the NeoNazis can say what they like!".
Which is the courts way of saying "it is illegal when we see it, we just leave some nominal loophole noone can fulfil so we don't go against the letter of the law". All of this is just a lot of court cases influenced by some elaborate schemes to pick the right court (LG Hamburg preferably). But unfortunately those stand as long there isn't an explicit law changing the situation. Which won't happen, because the exact same laws and especially judgements defend corrupt politicians against journalists.
Also, any kind of free-speech movement is a no-go in Germany because "buhuh, but then the NeoNazis can say what they like!".