Final Fantasy XV - over 10 years now was the as Final Fantasy Versus 13 planned title in development and it's finally out on PC.
People who have never played a Final Fantasy title will have no trouble understanding the game mechanics or story, since the game has almost nothing to do with the other parts.
(An exception are, of course, the Chocobos - it's not a FF game without Chocobos)

Plot:

You play Noctis Lucis Caelum, Son of King Regis, thus the Crown Prince and 114th heir to the throne of Lucis.
With his father's blessing, Noctis and the gang (Prompto, Gladiolus and Ignis) set forth from the Crown City of Insomnia on a road trip to Altissia, where Noctis is to wed his fiancée Lunafreya Nox Fleuret.
However, these plans fail as the Niflheim Empire deceives the Crown City and steals the kingdom's treasured Crystal.

Story:

Although convincing history and characters, there are quite a few flaws worth mentioning. Starting with the previous knowledge: If you do not know the anime series Brotherhood and the movie Kingsglaive, you will have many problems especially at the beginning. The invasion of Lucis will be dealt with in a few seconds, villains will be barely or not be introduced at all, and many relationships will remain unclear. Who is Lunafreya? Why is Niflheim really evil?
Even full cutscenes and storylines are inserted arbitrarily and make it unnecessarily difficult to follow the fundamentally interesting action.
I strongly advise everyone who is interested in the story to watch both the 'Brotherhood' anime and the movie 'Kingsglaive: Final Fantasy XV' first.
Aside from that, i think that the story is actually pretty decent.

Combat:

In almost every quest, you will fight imaginative and nicely designed opponents and unlike you would expect from most Final Fantasy games, this is no longer turn-based.
You attack the enemies in Real Time, even your colleagues attack fully automatic and without your intervention.
Even though you can literally play by using only two buttons, the fighting still remains somewhat tactically because Noctis can teleport with his sword to opponents - a "warp attack" and even use magic at the expense of MP.
The system is quite simple, but offers enough tactical depth to be able to act smart against particularly tough opponents
It's also possible, to take control of one of the other three characters when the relevant ability is unlocked in the Ascension menu.

Graphics and Performance:

So let's talk about the Visuals first: The game is really beautiful. The monsters look amazing and the LOD's are nearly not noticable. Probably half of the polycount went in the food tho.
This game makes me hungry everytime.
Since I am fine with playing the game in 1080p, it was no problem to run it on high settings with my quite heavy overclocked GTX 1060, a Ryzen 5 1600 overclocked to 3.8 GHz and 16 GB RAM.
On high settings the FPS stay around 50-60 the whole time.
The loading screens seem to be no longer than a few seconds on a SSD most of the time which is amazing.
I heard pretty often that people had better performance in the demo, but for me it was the other way around.

It has it's flaws, but it's definetly one of my favorite games.
If you are thinking about getting the game, then I strongly recommend that you try out the demo.

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Noctis: "Do you think this is a game?"
Prompto: "Sorta, just trying to level here, dude."

Additional Notes:

• Download size: 75.5GB Without 4K textures.
  
• Mod support - Fuçk yea!
  
• When 5.1 speakers don't work it seems like it would help to set partial spation off in audio menu. Also switching speakers to only play 2.1 in Windows helped some people.

Feel free to ask questions in the comments. I will do my best to help you, if I can.

Links:
The 'Brotherhood' anime series Youtube Playlist