The effect is powerful enough that its worth going for, but theres a lot of pieces here that need to come together before it works
Reanimate / Animate Dead [The Foundation of Reanimation Strategies] Reanimate and Animate Dead turn your graveyard into a shortcut
Mana is the most basic resource for activating cards , and mana is also required to activate numerous activated and triggered abilities other than cards
You build up your tokens, but need to give stuff to opponents to do so, and as long as you avoid giving them cards that cause them to lose, you'll get plenty of 5-star reviews
Magic is all about context, and you simply cant know that context completely until the entire contents of the set are public information
The efficient mana cost makes it very easy to cast Activated Sleeper after a board wipe to get a copy of the best creature that died or use it to pull off other tricks