We have just 4 rares making my Top 10, and one cycle each of uncommons and rares in my Honorable Mention spot, so that's 4.5 spots across 11 spaces
Its best when they dont know you have it, and you play it as a sorcery-speed removal spell
Nekusar is a powerful commander, which makes him unpopular, so be prepared to deal with some frustration
It effectively shrinks your deck so that instead of running 60 cards, you can run 56 (with some little timing hiccups)
It hits all the big scary things and has generally the broadest target range of the discard spells
With more card draw, you can control games with cards like Organic Extinction, play huge spells like Wake the Past, and get your big creatures and planeswalkers like Brudiclad, Telchor Engineer and Ugin, Eye of the Storms more reliably