it actually was pretty nice in my book, I wrote my thesis in Motif and I got it to run on several different unix platforms without a lot of issues. There were also some really nice commercial widget sets available, as well as things like XDesigner (iirc) for putting GUIs together.

Not saying it was super easy to use (took me a while to get drag & drop working the way I wanted, I even ended up subclassing XmText to get rectangular highlighting) but it sure was nice, I wonder what would've happened if it had not been commercial but had been available on an open licence to start with.