Its good for offense and defense. Just depends when the time is right. Since
Book of Moon is now limited in the Adv. format, i'd say that this card will be / has been seeing more play.
First off, you can use its first ability to put a heavy hitter in def mode, once it declared its attack so it cant change its position that turn.
Second, its quite good against beast down decks, especailly ones with Beserk Gorilla (put it to defense it dies.)
Also, in some cases, you can summon you monster (in example,
Sangan) use
Enemy Controller's second ability, sac it, and take control of your oppoents big monster and deal some damage and/or win the game, and lets not forgot, get
Sangan's effect.
One more thing is if you oppoent uses cards that target, like NoC, or
Brain Control, or
Snatch Steal, you can always use the second effect and take control of your oppoents monster till end of turn.
And lets not forget the nasty combo with
Soul Exchange.
These are just a few things that are possible, overall, I'd say that
Enemy Controller is a pretty nice card.