I looked at Vanilla a few years ago when it was in version 1 and didn't have time to look for further due to the fact that my first impression to Vanilla was this is a different kind of forum but I recently starting to rediscover Vanilla where it has been totally rewritten at version 2. Below is my review of Vanilla version 2.

Vanilla Wins Best Forum Software 2013

Vanilla is an open-source community-building solution. It is can seamlessly integrate with your existing website, blog, or custom-built application.

Vanilla has lot of compelling plugins such as Embed Vanilla, Single Sign On, Facebook Connect, Twitter connect, Google connect, and OpenID connect, etc

It still has the same look of the old Vanilla but improved, it does not look like the convention forum application but Vanilla is a forum application.

It has a lot of good features and good architecture, it takes after much best practice from many PHP frameworks, it utilizes MVC patterns and much compelling reason to use it like I already presented but it is not perfected.

Vanilla has the following areas that need improvement:
. It is a little confusing between Vanilla hosting application verse Vanilla open source application, the features that you see at Vanilla site might not be available in open source Vanilla and you can't buy it either. The only way to get the feature that you see at Vanilla hosting is to pay for their Vanilla hosting service
. It does not support site that runs in MySQL strict mode currently
. It frequently hit the famous "Bonk" screen if your site does not fit in with what Vanilla is expecting. The "bonk" screen need to improve a little to provide more information about the reason why it is "bonk"
. "cache" is not very flexible! If anything that does not match the "cache" it causes the "bonk" screen. The "cache" need to be more flexible to adapt to changing condition and recreate the "cache" rather than just hit the "bonk" screen.
. There are more that I see but these are the most major issues that I see as of now.