Thanks Steve, for also naming the other great additional mods available for SH3. I personally think NYGM is an astounding achievement. This man's opinion and I have been there and tried them all.
At this time SH4 also offers the simmer a great experience in Fleet Boats and in U-Boats. My advise jump in and try them all you cannot go wrong. The best thing is that there are some really neat things coming down the pipeline for SH4! Well 'nuff said and keep it all on the positive side.
Happy Hunting guys!