I remember I was searching using google, frustrated after realizing that MODx Revo back-end is not going to be any faster soon because it's based on ExtJS and it's heavy as hell. I didn't expect too much, because previously I was trying to find a CMS that would embody my vision of a good one, but was getting no results that would satisfy my needs. Every time I was finding something I felt like the architecture is not well thought out (MODx Evo) or code is poorly documented (Joomla) or that system is bloated and require a lot of hacking to get it working the way you want and its API is not intuitive (Drupal).
I was looking, first of all, for a reasonably fast CMS with a concise, intuitive API, custom fields and a simple back-end. So I googled something like this: custom fields easy api cms. Bingo!!!
After finding PW's website, I watched a video on the main the page and liked it very much. Ryan Cramer, creator of Processwire and a seasoned web developer with more than 15 years of experience, is really good at explaining how things work. I liked personal flavor of the video, maybe because I was tired of all that standard marketing stuff that you can find on CMS websites. I was amazed by the simplicity and elegance of the back-end (see demo here). I even began to doubt that it can really provide all necessary functionality. How wrong I was!
Then I proceeded to API pages and they blew my mind, I began feeling that I found a true piece of software/art.
Then I went to Ryan's personal website and took a look at the sites he made and I must say, I loved them. Island Hideaway, Tripsite and Directory of Scholars really impressed me, especially after seeing PW's minimalictic backend. I realized that PW is a weightlifter in the body of a ballerina :)
After downloading the source from GitHub and installing it (which was very easy), I started reading through all the articles on processwire.com and toying with PW for some time. The only thing that was a little confusing is templates vs. template files ambiguity. So I regestered on PW forum, asked my question and, after I quickly recieved very thorough answer from a senior member Apeisa, my last doubts gone. PW was exactly what I was looking for!
Now, after being a member of the community for several months, I must say it has very warm and welcoming atmosphere and the people are great.
If you still doubt, try it yourself. I bet you'll like it. And don't be shy to register on forums, you will find a lot of useful information there.
You may ask: Why would somebody want to make such a verbose review? :) Well, I can tell you why. I believe, that this CMS has a great potential and deserves to be known much more than it is at the moment. It hasn't been actively promoted (yet) and I hope that this review will help others find this excellent CMS.