Dangerous Waters is, without doubt, the BEST naval/submarine sim I've ever played, and I've played more than a few in my day. The fine folks at Sonalysts really did their homework when they were creating this game, since nearly every aspect of it oozes a level of realism that you're hard-pressed to find in most other games these days. I truly believe that the gameplay you experience in Dangerous Waters is a very accurate portrayal of actual naval operations and procedures in practice today; every vessel and weapon you will encounter has been meticulously reproduced according to real-life records. Hell, I could probably operate my own Los Angeles or Seawolf-class sub singlehandedly thanks to what I've learned from this game regarding their operation. Let it never be said that videogames don't teach you anything.
This tremendous level of immersion comes at a cost, however. Dangerous Waters is not so much a "game" as it is a genuine training siumlator, and as such has an extraordinarily steep learning curve that simply can't be overcome without first reading the manual and running a few practice missions as tutorials. However, even that won't fully prepare you for what you'll have to deal with once you finally take to the open seas, where even a single torpedo is usually fatal, and a compromise in stealth can ruin an entire mission. Dangerous Waters demands patience, dilligence, and a certain enthusiasm for submarines from its players if they hope to develop any real skill for it.
Dangerous Waters is not for the faint of heart, but it can be a very rewarding experience if you take the time to learn the finer points of its gameplay. You may have to lose a boat or two or a dozen before that finally happens, but that's merely half the fun!