Well, you might call it obsolete. But it still(!) runs circles around so-called modern systems when it comes to interface responsiveness, and elegance of OS design.
Whenever I have to struggle with Pain(t)ShopPro or, even worse, GIMP, I wish for DPaint, and MaxxonCAD might not be a contender for AutoCAD, but it was way easier (and more affordable) for casual use.
And the development environment around SAS C with its blazing fast compiler that could produce ass-tight code (Try making a "Hello World!" program in less than one K of executable on a "modern" system) is still on my mind. Especially with its support back then - far superior over what I get today with the different commercial development systems I use.
Yes, it might be obsolete, because it had no memory protection, but a MMU is not the solution for for all the problems out there. No memory protection also made interprocess communication way easier, and if you consider how well Amiga programs interact with each other via a system-wide AREXX scripting engine, the lack of an MMU is neglectable.
At least editor-wise I finally found something at least comparable to the decade-old super-duper-editor CygnusEd: Notepad++. The sad part is that NP++ does not run on Linux...