I've been playing Phyrexian Metamorph too as a one-of and I'm not convinced.
It's occasionally decent when it's unexpected, but on the long run, I'd rather have a 100% reliable creature threat, especially one that I can use my temples to cast.
Several times I happened to draw it in close games with a clean board state and nothing to copy...
Several times the fact that's its not an eldrazi would not allow me to cast it advantageously.
To sum it up, it's not terrible, but it can be a dead card, and it's rarely decisive.
I will be removing it from my list for my next event, probably switching it for an Endless One or a Warping Wail.
It's occasionally decent when it's unexpected, but on the long run, I'd rather have a 100% reliable creature threat, especially one that I can use my temples to cast.
Several times I happened to draw it in close games with a clean board state and nothing to copy...
Several times the fact that's its not an eldrazi would not allow me to cast it advantageously.
To sum it up, it's not terrible, but it can be a dead card, and it's rarely decisive.
I will be removing it from my list for my next event, probably switching it for an Endless One or a Warping Wail.