The first ZoE takes a while to get moving - it's very story driven for like the first half of the game, but ZoE 2 plops you right into the action, and the unfolding story is fantastic, the characters are awesome, and their nods to other Konami titles are awesome too (one of the Orbital Frames in the game is the "Vic Viper" from Gradius, and when you fight it, it plays the bonus stage music from Gradius - it's cool as shit)