Which spells do folks consider worth learning or upgrading ?

[Frank]

As a level 22 Warrior, I've used Bless, Weakness, Slow and Haste throughout and I just started on Phantom and Blind (awesome!) recently. At least for my playstyle, Distortion (lvl 2) >> Order (2) >> Chaos (1, used only to burn plants).

I agree with Sandsai that direct damage is less important than tactics in the late game, based on my experience with the Rage Box. I can do a lot of damage with Underground Spikes and Void (or whatever it's called), but it's always best to drop an Ice Ball in front of the enemy's archers instead.