The ADT approach does not replace full OO (and does make a compelling case for Wolfram Research to not offer fully fledged vendor-supported OO with IDE integration), but it's certainly better than nothing, and may be a good alternative if you don't want to rely on the valiantly attempted user-contributed MTools package.
In fact, because it's Mathematica, and has powerful pattern matching, the ADT approach offers a lot that traditional OO coding language can't. And remember:
And, it's also easy to model it in Systems Modeling Language v1 (SysML®), very useful! There is now a full slide tutorial trail section about the recipe, including SysML modelling examples:
And there is a summary of the associated Webel Policy notes (which are cross linked to the above slides):