In my 10+ years of experience as a web developer Wagtail is hands down the best CMS I've ever used or worked on. We've been using Wagtail in production for about a year in an organization with an annual budget of 4M. I thought winning over the content editors would be a challenge, instead they turned into huge advocates after the initial training.
But to leverage its full potential you really need to agree with the philosophy behind the technology. I've read other Wagtail reviews with the complaint that editors "cannot update the HTML code". This is by design. The philosophy (named The Zen of Wagtail) is in my opinion the best part of the CMS. You can read the official details here (http://docs.wagtail.io/en/latest/getting_started/the_zen_of_wagtail.html).
But to summarize:
The CMS should get content out of an admin/editors head and into a database as effortlessly as possible, the designer should call the shots on how things look (with html/css), and the programmer should be using a programming language (not a user interface).
That philosophy sounds basic: make things efficient for all roles involved. But it has lead to design decisions for how the CMS works that are just brilliant.
From an editor standpoint it is a dream come true. Every entry screen is custom coded to accept the data they need to enter. Custom data entry screens means the editor can make fast work of the task. And the editors I work with all agree that they really like this kind of system.
From a technology standpoint, this puts the programmer in control of a modern MVC platform that is designed to get stuff done quickly. And they get to use all the tools they're familiar with (git, python, database migrations, unit tests, etc).
The way the custom entry screens for the editors are built produce two outcomes: 1. they are ridiculously easy to build and 2. they keep all the design files (html/css) in a place that lets the designers modify them with ease. (We have web designers that do layout work.)
By recognizing the three roles and requiring them to work efficiently you get a race car of a CMS.
Wagtail is a relative new comer, and even a year ago I was afraid it was more of a toy than a mature software product. I'm convinced that it is not a toy. And the problems that it solves are solved extremely well. However, being new means there isn't the plethora of pre-built components that are available from the PHP counterparts. The Awesome Wagtail list is okay (https://github.com/springload/awesome-wagtail) but I really wish there was an equivalent to wordpress.org/plugins.
Wagtail is different from other popular CMSs, you need to reframe your thinking into the three roles: editor, designer, and programmer. Each role has tools to do their job very efficiently. One person can do/be all three roles and switch between them as needed. However, you need all three roles, including a programmer. If you don't have a programmer you need to find one. Or if you want to just click buttons in your browser to build a website then Wagtail is not for you.
Our business revolves around content creation and delivery. We've been able to increase the amount of content we can publish without needing to increase the team size. We also completed three very creative projects that we were previously understaffed to complete before the switch. We saw a big upswing in traffic through those projects and management informs me they were very successful.
Because we switched to python we are also integrating machine learning (TensorFlow) into our search systems that we would have only been able to dream about in our old system. This should further reduce labor, increase our capability, and integrate seamlessly into our wagtail search system.