I haven’t been using MODx for very long, but I have worked with several other content management systems previously and experienced both the good and the bad with them. MODx appears to be a fairly simple MVC style content management system with a bit of a pluggable architecture. I haven’t written any plugins for MODx, but it appears that hooks are used just like WordPress does.
I have found MODx to be very easy for creating fully tableless XHTML compliant sites and creating very search engine friendly websites. Very easily, it is also possible to hide what cms is running the site by using the easily created pretty urls. (There’s just a couple of simple settings and a file renaming.)
I found the templating system to be extremely frustrating because the template is actually stored in the database instead of in the file system like done in most traditional CMS. I really find editing the templates, snippets, and larger chunks extremely frustrating to edit in the manager because of the lack of syntax highlighting, and issues with formatting.
Overall, MODx doesn’t appear to be too bad for smaller boutique websites which are a large chunk of my current business. I believe I would recommend it to fellow freelancers for smaller websites that don’t have much need for plugins or high amounts of customization.