Compared to other spells like polymorph and multishot priests are cheaper in mana and don't leave anything on the field.
Apart from this obviously the mind control is absurd, if the games comes to 8 mana points you basically can't play a powerful minion of risking mind control over it and you losing the game right there.
I feel like the best balance change would be to increase the cost by one to the shadow word pain by 1 mana point and shadow word death by 2 mana points.
Mind control I've heard from Blizzcon that it would be balanced to 10 mana points, but so far nothing. That spell is just ridiculous to deal with, its way too strong. Either make it 10 mana points or have a limit to the creatures attack that it can take. If the creature has 7 or more attack it shouldn't be able to mind control it.
Mind Blast is also quite powerful, I feel like compared to Mage's fireblast its way too cheap for what it does. Again this spell probably needs to be at least 1 more mana cost.