I have Wolfpack and play it now and then. Thus far, I'm quite impressed. But I tend to be a bit of a lone wolf. The more single player features added, the more I'll be playing.
There would also probably be more interest if there was more scalable difficulty settings. I don't mind hardcore, I'm one of those types who own Sub Buddy and all that. But there are lot of players who might like the option to tailor their playing experience.
But overall, Wolfpack is definitely worth the money. I felt a great feeling of accomplishment when I sunk my first target. Great explosions too, LOL!
If you ask my opinion, buy it. You need it in your naval sim library.