This will be a quick one. I'll assume you've already seen Girls und Panzer and are wondering whether the OVA is worth checking out. If you haven't watched the show yet, it's best to watch it first but you could probably still enjoy this title on its own if you really wanted to. Although you will find a lot more to like about it if you're familiar with the original tv series.
The story takes place during the battle against Anzio, a "Japanese-themed Italian school". Be prepared for a lot of deliciously animated pasta.
Just about all the elements you loved about the show are here. The characters are up to their usual antics - Mako sleeping on the job, Saori being an air-head, and of course Miho whipping up moments of tactical brilliance when it matters most. Technically the outcome of the battle is already known to begin with, but this doesn't really take away from the watching experience.
Anchovy brings a (highly tongue-in-cheek) Italian flair to the mix, and there is plenty of humor to be found throughout the 40 minutes of screen-time. One of her generals is even called Pepperoni... Feel like a pizza yet?
The lead-up to the battle is plenty of fun and Yukari's recon mission is a highlight. However, the OVA really shines when it's time for the main event.
The battle is shown from multiple perspectives, and there's a plethora of strategy and mind-games going on as usual. This is the real magic of the Girls Und Panzer franchise: It's written in a way that balances comedy and action like almost no other. The viewer gets treated to a comprehensive view of the battle, and the quality of animation is even better than it was during the original series. The time and effort taken into making this OVA look and feel beautiful very noticeable and rewarding, particularly during the more intense moments of the battle. It must be difficult to balance such a vibrant colour palette with gritty tank warfare but somehow it all works.
As usual, tank otakus will probably relish the more intricate details to be found over the course of the OVA. There's also a fairly good balance of screen time for the main girls, so your favourite character will almost certainly get the time and attention that only you know she needs.
In short: This OVA is a treat. Side-effects may include a heightened enthusiasm for Italian cuisine, but it all goes away after you eat a good pizza. Panzer Vor!