More of a game than a simulator, and mostly for those who are interested in cold war naval tech and rudimentary tactics.

As some people already pointed out, it's not as detailed and doesn't involve micro-management as a game like U-Boat, it focusses more on positioning, the question of when to attack or evade, and shows quite accurately the technological leap the US/NATO made over the Soviets between 1968 and 1984 (the two "classic" campaigns), up to the point when playing as a US sub becomes a turkey shoot against the commies. Yes, the subs on the two sides are not balanced, because they never were balanced historically.
USSR more focussed on shoot-and-scoot tactics, they were louder and generally easier to detect, but also faster and often could evade torpedoes easier cause they could go faster and deeper.
US more focussed on listening first and building their situational awareness over time thanks to far superior sonar, and then positioning themselves in a way harder to detect, all the while their torps could go much further and had wire-guidance (which in terms of gameplay balance is almost like a cheat, compared to the USSR's torps, but that's just how things worked back then).

The interesting thing is the acoustic model the game engine uses. It's not 100% accurate in terms of the physics involved but sufficiently accurate to simulate real scenarios, even though the sound propagation paths are a bit simplified.
Also, even though a battle can easily last up to an hour depending on your play style, the acoustic conditions do not change during the battle, which is part of the arcade-y feel the game gives.

Mods
There are two major ones, one being "Epic Mod", and the other being "Dot Mod". The latter now being made by folks who worked on Epic Mod but decided to start their own project due to some beef I won't go into here.
Both add a vast number of playable subs on both sides, plus surface vessels, giving people an idea on how much harder it is for a ship to detect a sub, than a sub detecting a sub.
In general, Epic Mod increases capabilities on the USSR side, which has been met by some critics due to it not being entirely accurate.
Dot Mod puts out more regular updates and is overall more balanced, from what I could find on declassified performance figures of the tech involved.
Both mods add new campaigns which generally take much longer to complete than the stock ones.

Overall solid recommend if you expect a not-too-serious experience. If you want some solid micro-management and still have historical aspects, you might want to check out the game called "U-Boat".

More of a game than a simulator, and mostly for those who are interested in cold war naval tech and rudimentary tactics. As some people already pointed out, it's not as detailed and doesn't involve micro-management as a game like U-Boat, it focusses more on positioning, the question of when to attack or evade, and shows quite accurately the technological leap the US/NATO made over the Soviets between 1968 and 1984 (the two "classic" campaigns), up to the point when playing as a US sub becomes a turkey shoot against the commies. Yes, the subs on the two sides are not balanced, because they never were balanced historically. USSR more focussed on shoot-and-scoot tactics, they were louder and generally easier to detect, but also faster and often could evade torpedoes easier cause they could go faster and deeper. US more focussed on listening first and building their situational awareness over time thanks to far superior sonar, and then positioning themselves in a way harder to detect, all the while their torps could go much further and had wire-guidance (which in terms of gameplay balance is almost like a cheat, compared to the USSR's torps, but that's just how things worked back then). The interesting thing is the acoustic model the game engine uses. It's not 100% accurate in terms of the physics involved but sufficiently accurate to simulate real scenarios, even though the sound propagation paths are a bit simplified. Also, even though a battle can easily last up to an hour depending on your play style, the acoustic conditions do not change during the battle, which is part of the arcade-y feel the game gives. Mods There are two major ones, one being "Epic Mod", and the other being "Dot Mod". The latter now being made by folks who worked on Epic Mod but decided to start their own project due to some beef I won't go into here. Both add a vast number of playable subs on both sides, plus surface vessels, giving people an idea on how much harder it is for a ship to detect a sub, than a sub detecting a sub. In general, Epic Mod increases capabilities on the USSR side, which has been met by some critics due to it not being entirely accurate. Dot Mod puts out more regular updates and is overall more balanced, from what I could find on declassified performance figures of the tech involved. Both mods add new campaigns which generally take much longer to complete than the stock ones. Overall solid recommend if you expect a not-too-serious experience. If you want some solid micro-management and still have historical aspects, you might want to check out the game called "U-Boat".