Unique powers.
The problem with "useful powers" is "who decides it's useful?" Sure, we all love the decanter of endless water, but for a lot of people, that item is completely useless. They don't think of any way to use it creatively. I've played in games where one player reacts in DISGUST to the Immobile Rod he got (Which I more then gladly took so he could have one of my items).
Unique powers are, well, unique. It makes the item stand out.
The problem with "useful powers" is "who decides it's useful?" Sure, we all love the decanter of endless water, but for a lot of people, that item is completely useless. They don't think of any way to use it creatively. I've played in games where one player reacts in DISGUST to the Immobile Rod he got (Which I more then gladly took so he could have one of my items).
Unique powers are, well, unique. It makes the item stand out.