Rough start but hear me out
I bought it on day one and it was indeed a buggy mess but there are a few distinctions to make. We had a double release of a huge update for the base game and the DLC itself at the same day. This was likely a blunder because both, update and DLC, had their own bugs independently from each other and they added up for those who wanted to play the DLC. That's the devs fault, no way around it BUT since then the devs threw themself into it and released 11 patches in 7 days which apparently fixed the game breaking bugs. That's the kind of commitment I would like to see all over this industry. So I am pretty sure that the game will reach the status it deserves very soon and I am not willing to give a bad review for a few bad first days. But keep in mind that there are still unfixed issues and my rating is in advance that the devs keep up their efforts.
Contentwise you get pretty much what you expect. Another highly detailed boat and new historic missions. I wished for a more gear and mods for the boats like more versions of radio antennas, rubber buffer for noise reduction, several radar decoys (Sieglinde, Siegmund & Thetis) or anti sonar coating. There is a lot potential around which shouldn't be left unused. But despite that I like the new content. I like the boat, the missions and I like the atmosphere of being alone in the middle of an ocean with nothing under your boat but 5km of water. I recommend it.