Compared to PU this is cheaper, and can trigger multiple times. PU is only stronger if you assume your opponent is playing creatures that are stronger than the phantoms & are targetable. Plus you aren't using up a card each time this triggers, giving considerable card advantage.
Most creatures in this game are stronger than even the elite phantoms, and PU has one very distinct advantage over this - it can copy everything, including creature buffs and abilities.
Creature rushes are in fact vulnerable to many forms of control, so that's not a fatal flaw in this card. Permafrost Shield alone can slow rushes to a crawl or stop them if you're a little lucky. Bond decks with thorn carapace. Sexington's ragequit. Rainbows with sundial/firestorm. Even the dreaded shrieker rush is easy enough to beat with many decks.
These will not stack, and do not create phantoms retroactively for enemy creatures already on the field. Perm control being very common in player decks, if this is played against you, you can destroy - or even better, STEAL - it before playing many more creatures. The main balance mechanic of this card is that your opponent has total control over how many phantoms you generate.
And yes, "opponent plays a creature" is a weaker trigger. Nothing that happens on your side of the field will trigger this, neither will FFQ creature spawning, flying weapons, and boneyard's effect. Most decks do incorporate creatures to some extent, they are the most convenient and renewable source of damage, so it's worth packing a few to try and use your opponent's summons against him, but there are many counter-strategies to this card.
