APT's river cruise from Amsterdam to Budapest was excellent. There are interesting things to see every few minutes on both sides of the river all the way - and fabulous towns along the way and on the numerous side tours. The ship glides past fortresses, castles, quaint villages and point of interest (dozens of them) all the time.
But APT's 'Voyage Through The Balkans' is, at best, about 10% as good - especially if you've already been to Budapest and Vienna, which is by far the best of it.
There were no more than 5 interesting things to see from the ship in the 14 days - and most of the places we visited were drab and uninteresting - with only a few exceptions.