We've had exactly this experience over the last year, trying to use Rails Admin as a cheap way to build a content management system for a moderately large site

We've had exactly this experience over the last year, trying to use Rails Admin as a cheap way to build a content management system for a moderately large site with diverse types of content where we didn't really have budget to invest in building our own CMS. Rails Admin definitely excels at getting you running very quickly by providing a simple interface for CRUD actions around basic models. Where it falls down - aside from dealing well with relationships, as you mention, which is arguably hard to get right - is when you want to extend that basic functionality and provide a better or different experience for your users. We've had to create custom views for letting users control the layout of certain content types, including various drag-and-drop operations, and that was pretty unpleasant to achieve (one of those horrible times where you just end up hopefully copying from other people's projects because figuring out how to do it yourself from the documentation is just impossible); and we've ended up writing a lot of CoffeeScript to hack Rails Admin views to do what we wanted in various circumstances - much of this ended up very fiddly due to working with a quite weighty Bootstrap DOM. Lastly, the custom DSL, while clever, suffers from the usual pitfalls that plague these types of DSLs - your code can become quite bloated and re-use is very difficult to achieve. We have half a dozen models that broadly have the same customisations in Rails Admin, but we mostly ended up copying swathes of code from one to another because there wasn't a good way to re-use any of it. The documentation is also a bit hit and miss, and issues on the GitHub issue tracker are pretty much left to fester, sadly. In summary, I'd use Rails Admin again if I wanted an interface to allow experienced users to get a quick appraisal of, or make small modifications to, the data in a project; if I were doing something involving regular users again, I can't really say I'd consider Rails Admin a good option.