I'll let some of the others talk more about the features, but Frank's review is here:
http://www.subsim.com/ssr/dangerous_...view_page1.htm
The must have mod for DW is LuftWolf and Amizaur's Weapons and Sensors Realism Mod (LWAMI for short). It adds new models, and a great deal more realism. The official thread is here:
http://www.subsim.com/radioroom/showthread.php?t=83132
I have logged upwards of thousands of hours of gameplay and have never experienced a single stability issue; no freezes, lock ups or CTDs. I can even minimize it to do other tasks and pull it back up with no problem.