Wraithstrike is absolutely heinous, especially when combined with pretty common fighter/mage tactics. Wraithstrike, meet contingent improved blink (or contingent blink at lower levels or just straight-up blink at mid levels). Whatever you're facing, unless it has Uncanny Dodge, or See Invisibility/True Seeing (and your DM rules that it helps against blinking foes--blindfight doesn't), its AC=10+deflection mod+/-size mod. At level 15, that's a Cornugon dead in one round with attacks left over. At level 16, that's an angel of decay dead in one round with attacks left over. (By the time the character hit level 17, the campaign had banned the spell).
Full disclosure means that I probably should mention that I also arcane striked a top level spell, Power Attacked for full, and had a wounding weapon (which made a difference against the Cornugon, though I didn't try to argue that touch attacks bypass DR so maybe it canceled out).
Putting it and arcane strike on an otherwise core rules only NPC with meager equipment, meant that, every round, he took an fully prepped and healed PC from full hit points to nearly dead with unlucky rolls and from full to dead with average ones.
Now for the real question--is a spell that is that good for the people who actually use it (you know, fighter/mages with power attack, Arcane Strike, and good weapons and defensive spells) appropriate at any level? I think not.