Wall of Swords is simply amazing; it allows you to block all sorts of nasty units like paladins, nightmares, bears, and so on. At the same time, it sometimes manages to block archers, which makes it incredibly powerful. God is also a very good spell; finally, there's a decent offensive spell in the Haven faction. Crystal can indeed be used frequently to increase spell damage. Sorrow didn't impress me, but moving the wall to the Chaos faction is a good idea. And Hive, no matter what you say, is the most useless spell.