From what I see in the screen-shots the graphics look pretty good ,but they aren't really changed soo much from SH3-some new ,more "clean" textures,and some effects that were kind of poorly modeled in Sh3.I'm pretty confident that I'll be able to run it fine ,just like SH3.
I also would like to see some nice-looking crewmen,a little bit more "wear-and-tear" on the sub (that screenshot with the submarine is really cool) ,some more detailed rooms and less weird bugs when the crew-men are in the t-stance or their bodies/heads dissapear.Also,a bit more work on the damage textures would be in order
The water already looks pretty good ,so do the ships.The sub should be the "center of atention" for graphics improvements since you see it most of the time and interact with it most of the time.The other ships look fine in my opinion,and the only thing they need is a few more crewmen on deck and some lifeboats or other debris than boxes when they sink.