It'll take out way more spells than enervation if you've got good stats. Against a high-level caster (figure stat starts at 18, +4 for levels, +6 enhancement item, +3 or so inherent bonus = stat around 30-31; that grants a lot of bonus slots) it's horrendous. Not so much against a lower-stat caster, sure, but...
Still, on reflection, it's inferior to feeblemind, so...