IMO this spell is ridiculously strong. There is no other spell (or op) quite like it. 6 casts of ET brought me from 100% stealth to 27% stealth in about 30 seconds. Oh, and over the course of 20 hours, getting ET'd every hour on the hour, I've been able to use 3 single ops (and I've lost 300 honor points to boot). I understand that the core concept of the spell is to limit the power of rogues (halfers in particular) and the enemy is doing a great job at it.
I simply don't understand how one spell can be that strong, while there is no equivalent to do the same against mana.