Repostrd from the TV Show sticky thread -
"Just watched the special episode and for those who are considering watching Invincible Season 1 before Season 2 drops I wholeheartedly recommend watching this 'Atom Eve' prequel/origin episode before Season 1."
Would like to add - "Not sure if I'd suggest for it to be the 1st episode of Invincible new viewers watch, for those that haven't rewatched the 1st season in 2 years but remember the main plot points, 'Atom Eve' is a great episode to watch before re-watching Season 1."