I like how easy it was for me as someone who has little experience with functional programming languages, to start writing code in this language fairly quickly. It's also very fast at running my tests (in comparison to other testing frameworks). The documentation could be better but that isn't really its fault - rather than being written by people familiar with the software itself, most of them are just tutorials or blog posts from random authors. For example, there aren't any books out yet about using happstack for production applications, which would have been nice if you're looking into making your own website/blogging platform. If you want something simple and quick to get up and going then happstack will do what you need! We wanted a way to build our site without having to spend time learning new technologies we weren't already comfortable working with. As well as giving us some basic templates to work off when creating our own themes.