Cold waters is akin to what ace combat is for flight games, an "arcadey" game with enough realism regarding equipment, gear and mechanics,
Where the general gameplay is not at a simulator level, but you're able to do things you probably wouldn't be able to do irl.
Each submarine you choose will act different and will have different tools at your disposal to fight against the various enemies that also will have their own varried set of tools and weapons.
Nor does it take EVERYTHING into account like a lot of simulation games tries to do.
You could call it semi-sim if you'd like.

By no means is it a bad thing, The game is a lot more approachable to people that aren't so deep into the simulation style of submarine games, for example something like silent hunter or Dangerous waters

Each vessel in the game is modelled very nicely as well as the water looks great, which are the 2 things you're going to see 95% of the time.
The underwater seafloor is a bit barren, but given that it's not a primary focus, it's not as big of a deal, and whenever the combat takes place in shallow waters, there is some fauna to reflect that.
The combat in the open water can feel a bit empty at times, but does not ruin the game.

The game consists of 3 campaigns and some "single missions" said single missions are based on the variety of missions you can encounter in the campaigns (although it's usually to sink some sort of vessel).

Probably the most common played campaign is the one set in 1984 that follows a "what if" ww3 scenario in which the soviet union attacks western europe and you as a submarine captain has to prevent their shennanigans in the northern atlantic.
This campaign is great and is the best campaign to start out with for new players.

The 2nd campaign is the same scenario but set in 1968, given that a lot of the tools and mechanics one have gotten familiar and used to in the 1984 are missing, you now have to relearn and adapt to a more "basic" set of gear.
it's a great next step for anyone wanting a bigger challenge and loved the first campaign.

The 3rd and final campaign (disregarding if you install overhaul mods) is set in the 2000s and follows another "what if" scenario in which China attacks Taiwan where the player is tasked with defending the Pacific from Chinese vessels.
This campaign is both an increase in challenge from the 1984 campaign, and it changes the setting and opponent, giving it a nice bit coat of fresh paint.

One of the weird things is seemingly how the entire fate of the world hangs on the actions of 1 single submarine captain, and the rest of the armed forces seems quite incompetent at managing the war effort.
It's a bit funny, but nothing that ruins the game.

Gameplay consists of 2 parts, the campaign map and the "arenas".
Throughout the campaigns you'll be given a variety of missions that changes each time you play the game, which gives the game a lot of replayability.

The campaign map is both great and at the same time a bit scuffed.
The map will have icons depiting the various differnet vessels, you move your submarine around, sailing to various places depending on the mission and try and intercept enemy vessels, or sometimes get intercepted yourself.

However you wont know exactly where the enemy vessels are before a satelite or plane have been over that general area, and you'll then be able to hunt out your taget or fail to succed in you mission.
Whenever you fail the game will take that into account in the overall war.

The game is "dynamic" in that the war can shift back and forth based upon how much you succeed and how you fail. The fact that the war is dynamic makes the game more replayable as you'll not experience the exact same outcome the 2nd time you play the campaigns.

The biggest problem with the map is at times i've seen the enemy icons get stuck on the "geometry" and wouldn't move, which on the plus side made me able to intercept them, but it drags you out of the moment and kinda ruins the immersion, it thankfully did not happen often, but was something worth noting.

Whenever you encounter an enemy vessel, you'll enter an "arena" where you duke it out against the enemy vessels or you sneakily evade the enemy entirely and leave the arena.
The main meat of the game is in this arena and it does quite a great job of making the enemy seem competent and an dangerous opponent, even though there are things that seem to be a bit weird, like enemy subs just sailing around in circles, or that every enemy spamming the active search nonstop.

If you get bored of the vanilla game there are some large overhaul mods for the game called epicmod and dotmod that further expands on the game, but are also harder than the base game.
That might honestly fix the 2000's bug i've encountered, but i've not tried it yet as the mods themselves aren't without issues and bugs themselves.

I'd highly recommend the game if you're interested in submarines, the cold war or generall just think it looks interesting, even with the 2000's campaign unplayable for me, i'd recommend the game as it has been enjoyable enough for me already.

Wallpaper engine is quite neat in the fact that it provides you with what it advertises without being heavy on your processor at all.

It has a huge selection of wallpapers that you can use, from various genres and styles, it almost has something for everyone.

You can even make your own wallpapers.

Granted because of this, the quality of wallpapers can be mixed sometimes.

If you ever wanted a moving background for your desktop, i'd definetly recommend Wallpaper Engine