Enemy Controller is a great card for the upcoming format. Enemy Controller is a perfectly balanced card in the sense that he can be used defensively or offensively; stop the opponent's attacks or steal their monsters leaving them open for an attack. Between all the monsters that benefit from being in the grave and all the monsters that generate extra tribute fodder, Enemy Controller is indeed an amazing card that can win you the game.

As I said, Enemy Controller can be played defensively and offensively. On the defensive aspect he's able to stop your opponent's attacks. This saves your monsters and helps you preserve field presence, obviously. However, it is not the best form of defense. Compared to Book of Moon it cannot stop monsters from synchroing with eachother or stop monsters effects such as Lumina, Zombie Master, XX-Saber Gottoms, etcetera. However, what makes it an equally good choice as Book of Moon is it's ability to be seriously aggressive. By tributing a monster you control you can take one of your opponent's monsters until the end phase. Well, with cards that benefit so much in the graveyard like Dandylion, Plaguespreader Zombie, Necro Gardna, etc. This doesn't make tributing a monster a big deal. Again however, there is a drawback. You can only summon once per turn, so unless you already have field presence, tributing your monster to take your opponent's won't help you much. But alas, there are monsters that special summon multiple copies of themselves to allow you to abuse Enemy Controller to the fullest extent. Deep-Sea Diva and Rescue Cat are among such cards. Deep-Sea Diva special summons another Diva from your deck. This makes it seriously easy to tribute one of the Divas for Enemy Controller's cost to take your opponent's monster and go for a synchro summon. The same goes for Rescue Cat. You can easily grab X-Saber Airbellum and another beast monster, tribute the beast monster, and then attack your opponent directly forcing them to discard a card and then going for a synchro summon. As you can see, Enemy Controller is quite a dangerous card that can be an essential asset to you winning the game, always consider it when building your deck.