Yahari Ore no Seishun Love Comedy wa Machigatteiru. Kan: Dakara, Shishunki wa Owarazu ni, Seishun wa Tsuzuiteiku.

TL;DR:
It doesn't feel like another OVA nonsense made by a studio.

Considering this is a review of an OVA, I'd give it a higher score. Yes, I have to admit that this episode isn't any better than the TV. Though, it's still much better than most of the OVA from other animes, especially those spin-off ones.*1

Is this the main reason why I gave it an 8? Not exactly, but also…

Watari Wataru, the author himself, is the screenwriter of this OVA. The episode also follows the canon timeline. I know, it's still not canon, but I think it's also good to know some of the author's ideas ... after he finished the light novel. I really hope they could animate the "IF" storyline (Oregairu ANOTHER) as a whole season instead of just releasing some standalone OVA.*2

At the end of the day, it is just a one-episode OVA that doesn't spend you much time to watch. It's fun. Go give it a try. But most importantly, 「だから、思春期は終わらずに、青春は続いていく。」*3

Footnotes:
1. I enjoy watching spin-offs, however, spin-offs are spin-offs.
2. If you don't like the "IF" ending, it proves the true ending we got is the best.
3. My Crap Translation: Therefore, youth hasn't ended, youth is still going on.

Oregairu wasn't the same after Season 2 sadly.
First two Seasons were really something else. Oregairu Zoku was a masterpiece with so many great scenes it was so hard to beat by a mile. In the third Season, the direction went in a more romantic approach. However, it felt like the show only had the same name, but lost some of its greatness somewhere between the 5 years gap of waiting for the 3rd Season.
The same goes with this OVA. We have a continuation what happens after the finale of Season 3, but it looks like they just wanted to quickly wrap it up ... as a whole. At least I could enjoy my beloved music and some funny moments.
As a very huge fan of this show, I won't say I'm disappointed, more like a little bit sad they couldn't finish this show with the very last scene from Shin novel. To me, that was the true finale of Oregairu.

The third season OVA isn't faithful to the "Oregairu Shin" source material. While the main seasons stay true to the original light novel series, the OVA takes a different approach. It selectively incorporates and omits elements from the "Oregairu Shin" light novel, and also adds new scenes that weren't present in the original. You might notice that the OVA is a complete mess if you've read the "Oregairu Shin" light novels. It focuses heavily on Yui's character, while some of the elements that were originally intended for Yukino are either omitted or reduced. It gave everything to Yui that should have been Yukino's. In other ... words, THIS OVA IS JUST ANOTHER STUDIO FEEL'S CORRUPTION!

The OVA covers volumes 1-4 of Oregairu Shin.
Here's what's missing and what's changed in the OVA:

The Date between Hachiman and Yukino is being cut.
All the sweet phone moments between Yukino and Hachiman have also been removed.
In Shin Story, Hachiman completely rejects Yui for being too suspicious, while the OVA original had him resisting the urge to hug her. Additionally, the date between Hachiman and Yui never occurs in Oregairu Shin; this was an OVA original as well.
All the stuff that happened with Yui is well-adapted, while all the moments related to Yukino are left to dust.

The point of Oregairu Shin is to focus on Hachiman and Yukino's relationship. But if Studio "Feel" handles it, Their relationship may not Progress (in the Anime). Don't expect much from them...

And Don't Watch it If you're Yukino Fan, you won't be able to enjoy it. It's a Pain...

Japanese fans mostly favor Yui, so the studio basically made this OVA to promote the VN game, which again exaggerates Yui & Harem's route to get more money, cus why not? Though the canon couple suffers because of this...