I give this game a 6.5/10.
PROS: As my only Submarine simulator in my inventory, I will say my first impressions with this game were very good. I got hooked on sailing the pacific ocean, stalking my enemy before destroying their ships and forcing them to the bottom of the sea. Learning how to use the crew, their watch schedule and rotation, and watching them get promoted and recieve awards for their actions was the most satisfying part of this game for me. Each submarine performs differently and the missions you recieve can have very tense moments that had me sweating.
CONS: This game is not very well optimized and using time acceleration can be very dangerous as enemy ships and planes will appear of out no where and sink your ship. Also, after hours of gameplay all of my save files suddenly became corrupt and I am completely unable to play the game now. I would look into what went wrong, but I am playing other games now.
If the game had been fixed at some point during it's life then I have no doubt it would be one of the best Submarine games on the market.
If you are interested in this game, buy it when it is on sale and have fun. Just be warned that there are many problems that may make your experience aggravating.