Oregairu is the short form of the original title i.e. "Yahari Ore no Seishun Love Comedy wa Machigatteiru." (in japanese machigaeru means wrong) or "My Youth Romantic Comedy Is Wrong, As I Expected" in english. But don't get fooled by the title at all! The phrase "Don't judge a book it's cover (title here)" applise well for oregairu.
Our protagonist Hachiman Hikigaya or 8man (in japanese 8 means hachi) is a loner and also depreciates the idea of youth being full of joy and happiness. The anime isn't filled with lucky pervert scences as you'd expect from the title, instead it focuses on being more real. If you're bored watching run-down-the-mill highschool anime's then this one will really hit the spot!

Here's the plot of the first season :
Hachiman Hikigaya is an apathetic high school student with narcissistic and semi-nihilistic tendencies. He firmly believes that joyful youth is nothing but a farce, and everyone who says otherwise is just lying to themselves.

Yes, the OVA will be bundled with the game (developed by MAGES) of the final story as bonus, who's release date is unknown more

The anime is based on the light novels which itself ended with volume 14.5 on April 20, 2021. The final season or season 3 marks the end of the anime. Though it will get a special OVA episode which will do continue after the last episode of the final season, which adapts from the shin novels. But you may think that the shin novels may get adapted into a new season but they don't have much contents for the same.
Also the new project which is getting announced -ketsu- isn't the continuation of the main storyline instead it will continue the another novels

The light novel series ended with volume 14.5 on April 20, 2021. And the anime series aired it's 12th and last episode of the final season on September 24, 2020.

In the 11th episode of the final season, Hachiman and Yukino have a long conversation on a bridge, trying to convey their feelings in spite of their poor communication and socializing skills. The episode concluded with them being together

There are three seasons of oregairu, season 1, season 2 and season 3.

SNAFU in oregairu is a slang term used in english which stands for
Situation Normal, All Fucked Up