I bought both these games on Amazon the other day. I have Silent Hunter 3 and really enjoyed it, though unfortunately I kind of broke it with mods. The neat thing about the Sub sims is that for a total newbie like me, they are fun, but FREAKING HARD and yet there are people in the sub sim communities making mods to make the game realistic because they think its too easy O_o
I had heard about SH4 for a while, which is why I ordered it. But I also got IL2 Sturmovich, an older but very good flight simulator I hear, as well as a cheap joystick.
IL2 has a lot of spinoffs, which I am hoping are expansions. There’s also an extensive modding community. I’m guessing the flight sims (which I haven’t touched in years) have at least a steep, if not steeper learning curve then the submarine sims.