Well, I got it yesterday via FedEx. Installed it and was quite pleased.
But, to make this short, as of right now I really don't see any "great" improvements over SH3. The only difference I can see upfront is with this version, you control and "American" sub in the "Pacific" fighting the "Japanese" instead of controlling a "German" sub fighting the "British/Americans" in the "Atlantic".
Everything else works basically like SH3 did. Maybe better eye candy and the cosmetics have changed a bit, along with added options. (I have all my graphic options maxed out) But in my opinion, just a major patch for SH3.
Don't get me wrong. I'm not complaining. It still seems to be a great sub sim.
Just offering an opinion.

Maybe the more I play it, the more I'll discover. (?)
Cheers!!!