A classic in the genre. The missions may be canned (that is, have no random variation aside from units reacting to you), but the sim gameplay itself is great - when it came out it pretty much blew the competition out of the water. The graphics/presentation is still good and realistic for a 1997 game. You might say it has a certain charm, even. Just wait until it's on sale so you actually get decent value, and yes, it does go on sale.
Gameplay consists of navigating your vessel - an improved Los-Angeles class submarine - and achieving objectives such as sinking enemy ships and laying mines.
To get an idea of what it's like, this is a boat that mostly sails under the water. Your primary means of figuring out where in God's name you are involves bouncing sound waves off everything - which is called sonar as it sounds cool - because you sure as Hell don't have any windows. Don't think it'll be quite as easy as captaining a regular boat, either.
And that's just basic sailing. When you're facing enemy vessels, it can get pretty tense. Overall, it can make for a decent challenge.
You can also upgrade your sub and your crew between missions with earned points, and change your weapons loadout while in port.
You unfortunately cannot access any proper tutorials in-game. There are tutorial missions available to play, short tutorial videos in the game directory accessible from the splash screen and a comprehensive PDF manual included, though. The manual is good and the game is great once you've learned some and start getting the hang of it. The submarine controls themselves are sensibly laid out and easy to use once you know how - of course, this game made the Guinness book of world records 1999-2000 as 'most intellectually challenging PC game', and while I wouldn't necessarily call it the hardest game in existence anymore, the difficulty still certainly holds up. Having the assistants enabled helps.
That said, it is a 1997 game. It may not run that well on modern systems, even if it runs well on mine. The naval combat packs it comes in are rather pricey, too; you should wait for a sale.
FYI, the Steam version is the latest patched version, 1.08, initially a re-release of the game in 2006. Random fun fact: this game used to be published by EA.
The music is of special mention. It's around 8 or so MIDI tracks, and it's the sort of great suspense stuff you might hear from a more subdued Tom Clancy film. You can download it here
and get some of the songs from the game remixes in MP3 format from here
. They're very good and very appropriate.
You can also watch the special promo/press kit/B roll video they released for it here
. Pretty fascinating glimpse into the development, plus some gameplay on a period computer that's frankly laughably slow compared to the speed anyone buying this game now would get. Kudos to Valve and Sonalysts for having it on Steam.