The game can be obtained on GOG, however, the add-ons are still missing. Drakensang - Am fluß der Zeit (River of time) and Drakensang - Phileasson's Geheimins (Phileasson's Secret).
The latter was iirc. quite short, but for completeness it would be nice to have.
In general, all DSA (Das Schwarze Auge = The Dark Eye) (aka Arkania, realms of A.) should be made available on GOG.
Drakensang itself was one of the definitely better RPG games, that did actually add some of Aventuria's (Arkania's) atmosphere from the (in Germany) very popular Pen & Paper RPG "Das Schwarze Auge" (the dark eye, literally it would be the black eye, but this has a different meaning in English ;-) ). DSA is known to have a rich and living background world (though with few white spots on the map) and to not only foster hack and slash, but also interaction and non-combat skills.
Drakensang was, esp. once rid of digital restiction management, a good representation of the world (of course a computer game needs some adaptions) and in my eyes a very good RPG in general.