Dragonsteel Prime

I can see why Sanderson calls this a curiosity. There are elements cannibalized (and improved on) for the Stormlight Archive, and because this isn't canon, this particular story will never be finished in that form.

The bones are damn good, though. I love Sanderson in all his varied forms, but Stormlight is stylistically my favorite, and this feels very similar, even beyond the elements he plundered, and [You Know Who] is pretty much fully developed and the fantastic character he always is in his regular Cosmere appearances.

I would not recommend this before Stormlight, because it feels like it might pull a couple punches away from it, but it is an excellent read. It's also an interesting look at his process, to see how he built kernels here into master strokes in Stormlight. Well worth it for Sanderson fans, maybe not standalone material for others because you'll never get a resolution.