First, Help Scout gets major brownie points for "eating their own dog food" -- they are all about the Customer Experience, and they live up to this philosophy by delivering not only a very easy to use and modern product, but answering support inquiries right away (and thoroughly), and publishing an extremely helpful and insightful industry blog. So when you buy into Help Scout, you're not just getting a great software product, but also getting a great organization running behind it.
Aside from that I love how Help Scout does itself in fact deliver a great customer experience to our customers. It gets out of the way. Customers are not aware that we use it, in fact they believe they are emailing directly with me. Transactions are fast and lightweight, there are not many bells and whistles to complicate the process and slow down the support workflow. Help Scout made the hard decision to not allow custom fields on tickets, and while this at first seemed limiting, it has in fact allowed us to handle the ticket queue much more quickly, due to much lower overhead.
For delivering quick and helpful email support, I can't imagine a much better way to bullseye the task than using Help Scout. We've been very satisfied with it.
The Docs section of the product is a little bit underdeveloped, but adequate. It would be nice in that area to have more cohesion the way you'd typically find in a generic content management system (e.g. Wordpress). For instance, currently it isn't possible to move an article from one collection to another -- you have to copy its contents, re-build it on the other side, and delete the original.
That is my main complaint. In spite of that we have a full internal and external knowledge base hosted with the Docs feature, and it is adequate for our needs, if not exceptional.