It very much is. In summary, the original Pathologic had three characters you could play as. Pathologic 2 initially released as a sort of remake, with only one of the characters from the original playable, with the promise that the other two would be released posteriorly as DLC.
However, it has taken some years now (Pathologic 2 released in 2019) and the second route / character has only just been announced to be planned to be released in 2025. As I understand it, in order not to stunt their sales, what was originally planned to be DLC will be released as a new game (Pathologic 3), and I expect the final character / route will be released as Pathologic 4 or something of the sort.
While the original had 3 characters and 2 only has one, I do think that the world, characters and gameplay are much better realized in 2. The world is bigger, denser, more believable and weirder than it was in the first game. Which is why I believe that it's not necessary to wait for all three routes to come out in order to enjoy Pathologic 2. As it stands, even if the developers go bankrupt and no more games come out, I still think Pathologic 2 is one of the best games ever made and certainly one of the best stories ever told, regardless of medium. It is very much worth the purchase (or torrent, if you want to try it out) and does not require that you played the first game to understand and enjoy it.
Please change the "No" vote count to 1.5