For those that don't know, Aetherize is an Instant from Gatecrash for 3U that returns all attacking creatures to their owner's hand. But Aetherspouts is a somewhat better card because it returns attacking creatures to the deck for only one more mana. That's much more devastating for an opponent to deal with if it's a lot of creatures that are being returned.
Aetherspouts even makes your opponent decide which creatures go on top and which creatures go on the bottom of the deck. So, instead of simply giving your opponent their creatures back to their hand, you deprive them of all those creatures, making them have to draw them again. Then, they have to choose whether they want to draw those creatures again sooner or later. Plus, if any of them were token creatures, they are gone forever. Ouch.
In Standard, Aetherspouts gave Blue decks a nightmare for aggro decks to deal with in their arsenals. It did see some Standard sideboard play at the very least, as the perfect counter to ultra-aggressive decks. Five mana was just too much for Modern, though. So, since rotating out of Standard hasn't been seen competitively. However, in Commander, Aetherspouts has become a staple in many Blue decks, so this card still definitely has a home.