On it's own, Ruin is a joke, mostly because of the damage. 500? That's it? A lot of monsters can easily shrug off 500 damage at epic levels, plain and simple. The damage needs to be adjusted more to, say, 5000. And maybe it could work with some damage metamagics as well as item enhancements, if you really want to go that far. However, ruin should have a bit of a drawback as a spell that deals massive damage to a single enemy: 3d250 damage upon casting the spell. I believe that this spell should be more of a "I want to do a lot of damage, even if it comes at a cost!", with the chance that the caster will be totally destroyed if they have less than 750 HP or face other dire circumstances.