Yeah. I guess it is in part because many of them were built quickly during the war (I think that's also the reason that so many are overground, it's just quicker to build overground than to dig), and also there are limits as to how appealing you can make overground bunkers, that must have thick walls and lack windows. But another part is that generally the Nazi officials had a really rotten taste, at least if you are not into ugly megalomania with pseudo-nordic statutes and the like. Also clearly some of the concepts were deranged, I mean that huge bunker that I linked to as a prime example for their ugliness, was intended to be something like an autarkic fortress (it had independent electricity and wells for water etc.) where the people were supposed to hold out during a siege for months in case the city was occupied. That one is now afaik converted to office space, mostly for design, advertising and media companies (though I have a hard time to imagine that as a creative space) and there's also a dance club in there, but really I think it's a totally oppressive building.