The universe of X3 has become slightly more segmented due to some of the gates shutting down unexpectedly. As a result, some of the sectors are no longer in the game (particularly the bottom right side of the X3 universe).
Some of the more important sectors are now broken down into mini sectors (though smaller than a full sector in theory, they seem to be just about as large as a regular sector).
For example, Argon Prime is divided into four sectors, Argon Prime Alpha, Beta and Gamma. Their sector info has been updated to fit the lore of FL.

Rarely, you may find a few sectors accessible only via the dreadful Trans-orbital Accelerators. They mount to no more than a handful in the entire universe and in a lot of cases have a jump beacon.

You can also find unclaimed sectors and claim them.

The universe map is otherwise largely unchanged.

What I feel about it:
The sectors I visited often in AP are largely still there. I really like the fact that you can really tell the sub sectors are sub sectors because a lot of them share similar background objects like an eye-catching nebula or planet, but in alpha and beta sub sectors you see those objects from a different angle or position. “Choke points” and regional economy is much more than a mere concept now.

The economy in FL is much more stable than that in AP or TC, meaning the NPCs buy from and sell to stations more efficiently.

Faster, better shielded and with a larger cargo-bay, Armored transporters and their escorts now do a better job supplying stations than the power-crept regular TS and heavy TS ships.

Another reason is that FL reduces a lot of the early grind (like trapping you in a 64m/s ship in some starting scenarios) so you the player can make an economical impact early in the game.

You also get notification in the form of cheeky news whenever a station gets removed due to inactivity so loading an early save is an option if you really don’t like losing an important one.
What I feel about it:
I am all positive about FL’s economy. In AP it’s easy for an entire universe to not have an ion-disruptor forge 40 hours into the save file. In FL those end product factories are not immune to inactivity per se, but they generally will continue to exist. The early game anxiety to climb over the curve as quickly as possible so that I can set up trade ships to, literally, save the economy of this universe is no longer present. I love it.

In addition to getting access to most rare/prototypical ships (they can now be found just flying around), the TS-AT (armored transporter) and M7D drone carrier class has been realized.

Drones of different races have unique features that I would leave for you to find out.
Ship stats have been tweaked. TPs are faster, M6s are much more maneuverable (from turning at the rate of 5ish rpm in AP to 10ish rpm in FL) and M7s and M2s can now mount some weapons they didn’t have access to in AP as well as getting their stats slight tweaked. The beam weapons, previously unobtainable from regular gameplay in AP, are available to a lot of the capital ships and even a few corvettes.

You also have access to an in-game ship browser.
What I feel about it:
Great news. The devs understand what us space Uber men care about. Rare ship collectors will have field day, too. The M6 class probably saw the biggest improvement as they were too cumbersome for fighters and too fragile for anything larger than themselves. M7s are no longer pretty much identical to each other and some boring M2s are now more interesting with the guns they can mount. The M7D class is both fun to use and extremely useful. The fan favorite Boreas has been nerfed to fit its description, however, but most ships received strictly upgrades.
 

Largely just how it felt like in AP.

I have noticed more capital ships utilizing emergency jumps, which makes boarding trickier than before from time to time. The addition of beam weapons will solve a lot of the auto aim headache, if you can accumulate enough of them to outfit a ship.

M1, M2 and M7Ms now carry over 20 marines. Gone are the days when you need to transfer more marines from another ship nearby to capture a Xenon capital.

Rapid-response ships still exist in the game and behave the same way. I have also seen regular military ships jump in to execute security orders.

You can now remotely steal wares from ships and stations.

What I feel about this:
The addition of cargo-bay hacker flattens a large chunk of the curve as you can now steal capital-grade weapons to sell or use. Otherwise, fighting and boarding feels the same.

This is the area that probably received the most amount of improvement

This one section will never be able to list all the UI and ease-of-access changes that were made into FL, but if you have played and extended amount of X3:AP or TC, you are guaranteed to notice QoL improvements in terms of UI everywhere.

The HQ can now acquire equipment, a feature present in just about every overhaul mod of AP.

The CAG has been replaced by a station manager command. An improved CLS still exists in the game somewhere; I found it one day, it triggered my PTSD, and I exited the menu and could not find it again.

It is now arguably easier to set up stations but just like the old CLS and CAG, ships will exhibit weird behaviors from time to time until you investigate it, tear your hairs out, and play long enough to know exactly what is wrong.

The addition of the in-game encyclopedia is what I feel the highlight of this expansion. Not only is it hyperlinked, but it also shows in which sector the item can be bought (if it is a ware, ship, or station) and also the availability of there is a player property presence. It is the biggest game changer for me personally.

What I feel about this:
I salute the devs at egosoft as well as the contributors from our dedicated community to invigorate the 15-year-old X3 engine. X3:FL should be called as X3:FL:QoL :)

Instead of manually building (and positioning) 50 stations and applying complex construction kits 49 times, we now have quite a few options to quickly construct a complex.

Complex construction kits can now link multiple stations all at once, provided they are in range. Building an entire complex automatically is an option if your ship has the right software. Hiring Hephaistos Corp to do it for you is still an option, too.

In addition to all the above, stations can now be upgraded to XL size at maximum, providing you with 20 times the production output without forcing you to purchase and drag 20 stations to the site.

What I feel about this:
Huge reduction of chore and more options. What’s not to love about it?

This is probably the biggest area of controversy. In FL races are fiercely diplomatically conscious, if you know what I mean. Helping a faction IN ANY WAY will carry aftershock among the faction’s allies and enemies. Ubering a dude to the next sector will get you shot on sight in another faction’s territory.

We are also given a powerful tool to work out the situation, namely agents who can increase faction relations and gain access to equipment and blueprints either by engaging diplomatic deals or steal them.

Overall, you can befriend a few factions extremely fast and much faster than before. However, it also means that your relations with the factions’ enemies will drop to rock bottom in minutes and while you can technically play a balance game and try to please both sides, any large reputation swing will shoot the balance into space hell and create a chaotic nightmare. For example, if you accidentally destroy a Xenon Q in Paranid space, you may find all your satellites in Boron space destroyed, which is beyond frustrating.

I highly recommend just picking at least two factions to piss off right at the start of a game and treat them as Xenons for the rest of the game. In any given playthrough you can be either pro-Argon/Boron or pro-Split/Paranid, as other combinations will take tremendous efforts to maintain, and frankly, to me, just isn’t fun to play around.
What I feel about this:
Initially it almost drove me out of the game due to my frustrating attempt at maintaining a positive relation with literally everyone. After putting the game down for a few months (a blessing in disguise as a lot of bugs got fixed between version 1.0 and 1.3), I sat down and did two vanilla playthroughs and enjoyed them so much that I’m now writing this guide/review. Having 30% of the map being hostile creates a lot of unexpected events that are actually a huge pro for a sandbox game we play so much and a game where really nothing is going on. One unbiased downside to having hostile ships everywhere is the combat music playing 24/7 to the point that it hurts my ears. I may need to replace the few combat songs with something that’s more soothing to hear.

The story largely exists to explain and let the player experience jump gate failure and the effect it has on the X3 universe. There isn’t much of a plot or story and the story missions are created to give you a few handy tools for the early game.
What I feel about this:
I play the story to obtain a free M6 :/, which to be honest, is not an easy ship to board if you don’t already have another M6.

(Literally copied from a previous section) I salute the devs at egosoft as well as the contributors from our dedicated community to give us X3:FL for free. It is a complete upgrade over vanilla AP.