Well, I was invited by name to participate in this thread, so it would be impolite for me to decline.
Disclaimer: I'm the line developer for Werewolf: The Apocalypse, and have been for the past, oh, five, seven years or so? Something like that. So understand that I have a personal bias for Werewolf; it's my day job, and it's the World of Darkness game I like best. On the other hand, I promise I won't freak out if people say it isn't to their taste — like all things RPG, tastes vary.
But that said, here's why I dig Werewolf.
First of all, the game is one of animistic horror. Animism, by the way, is the cultural belief that animals and plants and even sections of countryside have spirits; Shintoism is sort of animistic, if I'm getting the reference right, and lots of cultures have had their start with animistic beliefs. Now, the extrapolation of this concept with the World of Darkness is that if everything has a reflection in the spirit world, and the World of Darkness is more of a hellhole than our own, the spirit world is going to be a dark, dangerous place. This basic concept lays the foundation for a lot of different stories. What would the spirit world be like in the shadow of a concentration camp? A laboratory that counts vivisection and animal experimentation among its tactics? What about in urban sprawl? The animistic angle of the game can really engage a thousand and one stories, played right.
Second, like most WoD games, Werewolf taps into specific cultural references for its feel. Vampire is rooted in Old Testament Biblical stories (twisted around, of course), Mage in philosophy and all kinds of occult legends, and so on. Werewolf draws not just from European legends of werewolves, but also from most shapeshifter myths from around the world — African leopard-men, Japanese fox-women, Polynesian shark-shifters, and so on. But it's also a game about culture heroes like Beowulf, Heracles, and the like. The Nordic influence is pretty strong, too — the "Apocalypse" referenced in the title is more Ragnarok "Final Battle at the End of the Earth" than "world blows up," at least as the protagonists see it. It's very old-school.
Third, Werewolf is a game that really encourages players to work together, to think of themselves as a pack rather than a loose collection of sort of like-minded people. The Garou have a strong culture of their own, and they're social animals. There's plenty of reasons imbedded in the game for characters to not only work together, but to lay down their lives for one another. The werewolves of the WoD are a society that's been fighting a shadow war for years, and there's something about that "soldier" mentality that's rubbed off on their culture.
These three concepts lay the groundwork for a lot of interesting stories, or at least the stories I like. The game does involve a long look at heroism, but the concept of "hero" is pretty open-ended — is a werewolf who'd wipe out a whole town full of people for the "greater good" of preserving the Earth a hero? Is the werewolf who chooses a more humanist philosophy really in the right? Is it right to kill everyone who smells of "the Enemy"; where's the balance between genocidal rampages and standing by and letting evil prosper? There's a lot of philosophy to the game, if you want it — but, as other folks have said, that doesn't preclude action. At the heart of it all, you're a nine-foot killing machine with a heart full of fury who can manage to look human if you want to — but you aren't a human. Nor, necessarily, do you want to be — but that's up to the character and the player in question. If you like those European myths where the werewolves are the baddest things on four legs and humanity cowers in their huts for fear of the Big Bad Wolves, there's plenty of room for doing that in a modern context.
It's a big game, really. I could ramble on until everyone lost complete interest in what I had to say, and I don't know if I could cover it all. There are so many options, and they're often presented in the question of where you want to find your balance. Human or wolf? Flesh or spirit? Warrior or shaman? Tribal feuds or tribal alliances? These aren't binary, yes-or-no questions, and there's just so much room to customize your character and the game around them that it can almost seem like too much.
But that's what I like about D&D, too; you can do so many things well with the general game that you never have to play it exactly the same way twice. The main difference is that Werewolf has a few specific themes built-in; but I think they're pretty cool themes, so that suits me fine.
Sorry for the extensive ramble. Hopefully some other folks will chime in and maybe be a little more succinct (and for the record, fellas, don't think I didn't appreciate your kind words on the other thread. It was very, very gratifying).
And by the way, Mercule, thanks for being open-minded about the whole subject. Even if the game isn't ultimately to your tastes, I hope you can at least see some of the different things that bring other people back for more.