Television documentaries often work best when one knows nothing about the subject. Then the basic information can be interestingly new and the interpretation thought-provoking.
Art documentaries have their own aspect, showing both the (sometimes too) familiar and the excitingly unknown, with artworks and places one hasn't seen. BBC4's current series on Art Nouveau in Europe kicked off with a sort of introduction in Paris, showcasing Mucha, Lalique, Galle and Guimard and succeeded within those limitations and those of the presenter Stephen Smith (a 'cultural correspondent' of whom I had not heard) with odd pronunications, including Gismonda, Beranger and Art Nouveau with a voiced t.
To some extent like an Antiques Roadshow spin-off, the best part was the visit to Castel Beranger (in view of above comment, apologies that this blog does not explain how to add accents) or at least its entrance hall, as residents went about their daily business. it would have been good to see inside an apartment, but maybe they are too much altered, or maybe just too much, as Smith said of another over-preserved interior. Art Nouveau is often perilously grotesque. Another besetting sin of TV art is more talking than showing: one wants camera-work that mimics the eye's revealingly slow travels between full-view and details.
From the trailer, the next episode is set in Britain, so one partly knows what to expect - Glasgow and presumably stile Liberty - though hoping for new discoveries. There are only three programmes, so Belgium, Austro-Hungary and Catalonia may be rather squeezed.