I tried to copy some spells from a warlock, and i must say i am very disappointed. Metamorphosis doesn't cost mana, fel armor didn't work, Soul stone didn't work, demonic circle didn't work... basically no cool spells work. Guardian of ancient kings and inner fire doesn't cost mana either... And damaging spells/healing spells are a joke because you have no spell power. Yes metamorphosis may be the most OP thing you could ever copy, but honestly what are the odds of that happening? Every good player will notice when a DK has cast this spell on you, so they will just give you the most crappy spell they have. like this:
priest: Mind soothe
mage: slow fall
warlock: soul link
druid: soothe
shaman: water walking
paladin: Hand of Reckoning
What also sucks is that it has a 1 min CD compared to spell reflect which is a lot better anyway since it reflects the spell for full dmg, while you avoid it.
If blizz wants to increase the usefulness of this spell they should remove the RP cost and remove it from the GCD. Sucks that you have to spend 20 RP on it when you most likely are just gonna get one of the spells i mentioned above.
I'm not saying this spell is useless. Of course sometimes you manage to use dark simulacrum on a warlock right before hes finished casting fear, and you use AMS at the same time to avoid it while you fear him back. Or death coil, deep freeze, hammer of justice etc... but again, a warrior can do this every 10 sec while avoiding it at the same time.
btw, can you copy windfury, paladin seals, rebirth, totems, resurrection spells, portals/teleports/conjure food, and how long to they last?