Legendary pieces always have a purple/red name and a colored outline around the piece itself. They often match the effect of a non-legendary piece, but are either stronger or have added effects. You also can't upgrade them at anvils.
I think part of the joy (for me) is changing loot half-way through a run to better fit what's coming at me. You get a lot of the material you spent upgrading back, so it is sometimes advantageous to change!
Thanks... There's a few different colors used in item descriptions, and I haven't quite figured out which color is which.
Yes, the gear evaluation is a fun part of the game--it's really fun to realize, "OH, this will do X to my attack, and since this other piece of gear grants me an attack when Y happens, these two pieces of gear result in..."
This all leads me to want to maximize more and more, further and further...
Slight correction: Every item has a base version and a legendary version! It took me a while to realize that, too, then I later saw that it's stated explicitly in the last bullet point of the game features list.
There are also golden anvils that will turn a base item into its legendary version. I don't know if anything causes them to appear, or if they're just random. I've only seen one so far out of 25 runs.
