We've talked about goblins before, and our guesses weren't too far off. There's a new group of goblins (which is to say, not from the Steemwheedle Cartel that we're used to dealing with), which is joining up with the Horde out of desperation rather than profit. Goblins aren't used to needing other races' help -- ever since they overthrew their troll overlords back in ancient times, they've been masters of their own destinies. Now, they're second fiddles to the orcs and all the other races who've been established in the Horde for a long time now.
So in addition to all the cunning archetypes of tradesman, cheat, mad-scientist and everything else we've come to expect from goblins, we have another element of dealing with the betrayal, desperation, and loss that forced them to join the Horde in the first place. These are not new issues for Horde races, even if they are relatively new to the goblins themselves -- perhaps this was the one aspect goblins needed to become true members of the Horde, which they never had before -- a crushing loss that shakes them to the foundations of their identity.
I was wrong when I guessed that the playable worgen would be from their original home dimension, wherever that is. I even guessed they would be from the Emerald Dream, and to my knowledge, a relationship between the worgen and the Dream hasn't showed up either. There is most certainly some sort of connection to the night elves and druidism, however, and time will tell what the exact nature of that is.
The worgen we play are closer to what we normally call werewolves -- people who suffer from a transformative curse -- rather than the "actual" worgen from another dimension that first appeared in Kalimdor, although hopefully the starting quests in Gilneas will bring these two elements together in some plausible way.
Still, maybe it's ultimately cooler for the playable worgen to be like werewolves -- that gives us two forms instead of one, and it gives us more to relate to as well. Ask me to roleplay a wolf-like alien species from another dimension, and I won't really know what to do until I do a lot of reading. (Incidentally many roleplayers with draenei characters had trouble with this as well, often playing them in ways that didn't fit the lore until accurate knowledge about their characteristics and origins became more widespread.) But if you ask me to roleplay a man afflicted with a curse that turns him into a monster, that's much closer to home. I can take inspiration for my character anywhere from The Incredible Hulk to Wolverine, to say nothing of Professor Lupin from the Harry Potter series, or even the main character of An American Werewolf in London. The theme of "the beast within" is a profound one for all sorts of stories with a ton of interesting opportunities for roleplayers to explore in the game.
This is especially true for worgen druids, whose "caster" form is still quite beastly whenever your character is in combat. Your character could be a normal human librarian, street-sweeper or whatnot, until danger arrives and he or she suddenly turns into a wolf-man, then a bear, then a cat, then a tree, then a weird wolf-eared, owl-faced, teletubby-shaped creature of moonfire-spamming death! Well obviously you can't have all those forms in just one talent spec, but still, that's a lot of different forms! Combine that with a normal human form you can stay in out of combat and you get a lot of possibilities for fun roleplaying.
A worgen hunter has good potential too, since he can use the actual "Beast Within" ability to become a big red worgen whenever he likes, combined with the human-worgen shifting ability, such a hunter could express emotion very graphically.
If worgen could only be shamans, then they would be able to shift between human, werewolf, and ghost wolf forms and create a whole spectrum of wolfyness. Oh well.