An extra turn might not seem that amazing considering you won't have much mana left the turn you cast this, but the real power is that it gives you the opportunity for all your other creatures and planeswalkers to provide extra value
Whenever another creature you control enters, Kefka Palazzo deals 2 damage to each opponent
Being able to return creatures to the battlefield each turn, even in lieu of haste, is going to ruin a lot of opponents days
Its certainly a chaos card by nature, but as one of the best Polymorph effects in Magic its chief function is to be broad and efficient removal with a wildly inconsistent drawback
Players collect points by first playing (win or lose), bringing a friend to game night or teaching someone the rules, then redeeming those points for a chance to win a prize
Thats water bug and diving beetle erasure if you ask me