None There isn't anything like cod zombies on the idevice. There are many that claim to be similar but fall way short in every aspect.
No it's not. Before the $1.99 was worth it, but not anymore. The Dev just officially announced he's going to completely abandon this game.
Dead Strike isn't better as a game, but if you compare the Dead Strike team to the humongous Activision team, it probably took more work to make. But if you're deciding which game to have, regardless of price, COD Zombies definitely for controls, camera, violence (in Dead Strike, the blood is a bunch of red squares), weapons, and graphics. Edit: Woah, just found out there's gonna be a multiplayer! That should raise Dead Strike's value a pinch.