Emacs 19 was a model of low-defect, stable software, and my experiences reinforced that widespread notion. Over time and subsequent major releases, it grew and grew, and the complexity got too big to perform adequate QA, now nearing the point of unmaintainability. I also love it and use it daily, but I really wish the developers would show some restraint when considering whether to add new features (i.e., packages).

Having said that, the very core text editing engine, i.e., the part that's written in C and the basic Elisp editing functions around that are still rock solid as always, and for me this is still the ultimate model of what a text processing engine should be. It handles large files beautifully (and errors gracefully when it cannot), does file locking well, goes to great lengths to ensure the integrity of your file, all of that basic core stuff is just superb and well thought out, by a lot of brilliant people over a long time, and that's all very well optimized. I think the problem is that too many third-party extensions are included with the core release.