I wouldn't want to let onkelyogi's review stand unanswered, because I think his is a minority opinion. The record-high ratings (one in ten Germans watched this TV mini-series and the audience for the last episode was even bigger than for the first) and the very positive user reviews on amazon.de and elsewhere are proof enough that the majority of Germans really liked this show. In my opinion it is one of the best German mini-series in the last 10 years - an instant classic - and it doesn't have to hide behind series like Downton Abbey and similar shows.
Downton Abbey has better/wittier dialogue and may be a little more subtle, but Das Adlon certainly is more emotional and some scenes (such as the courtroom scene in the last episode) are truly sublime.
By telling the very personal stories of a few interesting characters over several decades, the script somehow manages to paint a picture of the general German history in the 20th century. The story stays true to the historical facts and the fates of the (real) Adlon family are cleverly and believably interwoven with the fates of the (fictional) Schadt family. You really care for these characters and all of them are played very well (I really couldn't single out one of the actors; they're all wonderful).
Das Adlon is very lively directed by Uli Edel (Christiane F., Last Exit to Brooklyn, Der Baader Meinhof Komplex), the cinematography is beautiful and the production design and costumes (which are well chosen for the different epochs) are sumptuous. Several of the actors age in their roles from adolescent to middle-aged very credibly thanks to the excellent make-up.
A final word about Wilhelm II.: In my opinion the Kaiser was portrayed pretty accurately in the series. For all I know he really was something like a caricature of himself in public and he was arguably the worst of the nine kings Prussia ever had (to the misfortune of Germany).
