I played it during the beta and only bought it to give a review.

Tl;dr: This is basically the worst we could have gotten, unlike the amazing base game, this adds nothing of value to the game and I will explain why. Even for free, I don't want it.

This review will be split into two parts: First, what you get and second, what you don't get.

This DLC adds 3 main things:
1. worlds with water
2. maritime trading houses (MTH)
3. amphibious enemies

Let's start with the last item, the amphibious enemies:
Amphibious Enemies basically means that native wildlife have a checkbox that allows them to travel across water fields, nothing more. This DLC doesn't include naval units at all, even MTH doesn't have "real" ships and your own units can't travel across water fields. Therefore, you can't destroy enemies, with conventional forces, that are on a coastline (but still attack them wir airplanes and artillery), which ultimately just adds to the boredom and is annoying after a while.

MTH, portrayed as something like "the Hanseatic League," are nothing more than pirates. Every new event or "mechanic" (I put them in quotes because they are either pre-existing ones that have been only slightly modified, or very shallow new mechanics) is based on the MTH. Unless you hop from island to island, you can completely ignore them, with the exception of the MTH pirate invasions. Aside from the logistics contracts that allow you to transport goods and troops to the islands (basically a strategic move), which costs an extreme amount of credits, they offer no benefit and are basically a nuisance and a waste of money. "Stock trading", for example, requires hundreds to thousands of credits per share and then has that money returned to you in dozens to hundreds, give you Information (unsure which Information or how useful they are) and make future contracts cheaper (although you will to calculate if you save any money with this tactic). Based on this, buying stocks makes no sense because you're either too poor to spend money on it, or you make so much money that it doesn't matter anyway.
That being said, this is a good point to talk about "logic". This game, set in a post-apocalyptic scenario where people are desperately trying to survive to the next day, has a stock market....a stock market in which governments invest taxpayer money to entities that are simply put up with. But that's just one problem with the MTH. The MTH is an invincible power that "masters the waters" and has bases in unreachable places. That's the justification for not being able to create naval units or do anything with water. No, I'm not kidding, I was generalizing the developer's even more ridiculous explanation. So you can conquer the planet, have hundreds of thousands of people in your army, have super heavy tanks with nuclear propulsion that would realistically use naval guns, and an air force that can bomb half the world in one turn, but even the idea of a dinghy is just not possible for you because the MTH would destroy it instantly. Not to mention that the oceans are one of the most important parts of human civilizations and cities as they enable things like trade.

The MTH's "naval warfare" is also misleading at best. Each MTH has a number indicating how many ships it has, and sometimes you get a cutscene at the beginning of your turn saying X ships vs Y ships, Z ships sunk. And no, that's not an exaggeration.
At best, the MTH "trade" changes the trade calculations and that's it, you won't notice any real difference in gameplay or consequences.

The last thing you get from this DLC, the best part of it, is the new planets. The downside is that when you play on a DLC world, you have to deal with the amphibious enemies and MTH, which is not worth it.

Now for what you don't get:
- No naval units
- No naval mechanics
- An extremely limited amount of MTH-based events (were you have to decisions on in your turns). What you don't get is: CEOs (as the ingame entity CEO) colliding with MTH because you want to spread out on the water, tsunamis, floods, citizens on the water who are in danger and need to be rescued, non MTH ships that have run into cliffs, etc.
- No new units
- No new techs
- No new buildings next to the docks
- No underwater areas
- No new tiles for water like reefs, corals, sand banks, cliffs, currents