Last year's Promi Big Brother rated quite well actually, despite airing quite late on most days (some of them started around midnight). It's been the most watched season in 4 or 5 years, depending on what audience measurement you base it on. It was the civilian season this year that didn't rate well on TV at all.. (but official word is that they were happy with its performance online).
I think people's reactions to last year's season was mixed but slightly more on the positive site. I think a majority expects a season like Big Brother 5, which had the most extreme rich/poor divide and huge challenges and last year's Promi Big Brother was none of that. But the return of the live feed created some hype before the season and that moved the initial talk away from having only one house.
The cast was received rather well (despite looking not that great on paper). I think some people got convinced that one house can be the better choice because some of the conflicts wouldn't have happened if people just lived isolated in their own house. I don't think anyone missed a second house by the end of the season. Some of the conflicts were carried by a strained pre-existing relationship, which I think worked for the show but divided the fanbase.
People also reacted positively to having a "Container-Chef", some sort of HoH that was either picked by viewers or the housemates and had some changing power over nominations (especially in the second half). Another feature that blatantly ripped off from I'm a Celebrity but got positive feedbacks are the "Nachtwache", the night watch. On IAC (at least in Germany), pairs of two have to guard the fire all night, which usually leads to interesting discussions or sometimes a bitchfest. They now have to do that on Promi Big Brother as well but instead of guarding the fire, they have to press a button every 11 minutes or it sets off an alarm in the house.
What didn't work out were the mechanics involving food and competitions. They had a small budget of usually 1 Euro per person and that had to be spent within 60 seconds. But they were only allowed to keep their food if they managed to win a game afterwards and they usually failed. So all they had was oats and water, which resulted in hungry housemates that were sometimes just lounging around because they haven't had the energy to do anything. The games were also extremely crappy and I don't think anyone liked those. (They somewhat listened to the fans here though. We don't have the details yet but housemates will compete against each other in the live games again.)
All that said: Are Germans convinced by the back to basics approach in general? I don't think so. It worked for Promi Big Brother, but it didn't work for the civilian season. People complained about people just lounging around and not getting enough stimulation besides the weekly task. So that one might have been too stripped down for German fans.