Wormhole is good basically in the same scenarios that Regifting Zombie is good (and Regifting is getting nerfed, so you know such scenarios must exist).
Basically, if you have a fast deck or a deck that can use a lot of cards efficiently or at reduced cost (or you’re playing cards that benefit when a lot of cards are played... like for instance Unlife of the Party), Wormhole is probably a good bet. It has an above-average body at three, Bullseye (which is just bonus), and has the potential to accelerate the game (which you want, if you have a low curve and often find yourself empty-handed).
You will want to avoid Wormhole if you’re playing a high curve (lots of 3, 4, 5+ cost cards), control (because your opponents aggro will overwhelm you), or probably if you’re already playing a lot of other sources of card draw (because your opponent will probably find it easier to empty his/her hand and get more benefit from its bonus).
Parting thought: if you’re not playing aggro, if you’re not SURE your deck is aggressive enough to take advantage of Wormhole, I would steer clear. A lot of plant decks play cards like Whack-a-Zombie. Now, if your Wormhole draws removal it was worth playing. But if your opponent has that removal you may be up a creek, because now he/she can decide whether or not to keep Wormhole on the board based on what is happening in his/her own hand. In other words, you change the tempo of the game by playing Wormhole, but if you play into removal you allow your opponent to choose the tempo of the game. Allowing your opponent to choose the tempo of the game is rarely good.
