IMO this is unquestionably a good thing about German law. There have been a few rare cases of "rogue police officers" (there was a case a few years ago where a police officer tortured a suspect because he wanted to save a child, which led to a huge debate about the morality of it all over the media) but the system seems to be good at making those the very rare exception.
Of course evidence still retains its context. An admission made under torture, for example, is likely to be considered inherently invalid because it is extremely unreliable. This is actually a bit ironic (Morissettian irony, not literal irony) if you consider that the US is engaging in systematic torture to extract bullshit intel out of terrorist suspects (whereas reliable evidence provided by a police investigation could be dismissed because of mere formalities).
Of course evidence still retains its context. An admission made under torture, for example, is likely to be considered inherently invalid because it is extremely unreliable. This is actually a bit ironic (Morissettian irony, not literal irony) if you consider that the US is engaging in systematic torture to extract bullshit intel out of terrorist suspects (whereas reliable evidence provided by a police investigation could be dismissed because of mere formalities).