Talking with some guys trying to merge V:tDA atmosphere into the NWoD ruleset, we got off on the various roads/paths and why some work, but most fail. Not the rules of how they fail, but how they fail players, or players fail them.
Yes, there are inherently flawed paths (Paradox, Typhon, Heaven) and paths that are intentionally created to be self-defeating (Evil Revelations, Service), but most that fail (whether the path itself, the player, or a combination of the two) are simply missing one key element that isn't found to be missing until several chapters into a chronicle. The rules are simple: a central moral focus, a hierarchy of sins, and the Conscience/Conviction and Self-Control/Instinct question. That's it rules-wise. Paths typically only fail at the roleplay.
So, what is required for a good road?
I think the best way to do this will be to examine the concept of roads, what they mean and why they are chosen, from both the players viewpoint, and also the characters.
Players who choose a road other than Humanity typically do so from one of three reasons (in my observation); they want freedom from consequences for their characters intended actions (Path of What I Was Going to do Anyway), they want to be obviously different and unique without needing to come up with a way to be so (Path of Sparklypoo), or they want to explore a different moral outlook (Path of What Happens If...). I have also twice seen a path selected because it truly made more sense given a characters background (Path of the Sire).
What does a road mean to a player? Obviously, it means freedom from Humanity. It means a character can be a monster, it means they are different.
For some players, it means that the character is inhuman (not monstrous per se, simply exceedingly different. No longer human) For some, it means being required to follow rules that the others don't understand. These last two are the only ones I care about as an ST. Just me. White Wolf is not for casual players, I have a Thursday Pathfinder (read: DnD) group for that. So, why was Zakai so angry when his hamburger came out with cheese? Why won't Laila go to the movies with the rest of the school band? Why does the old rancher on the far side of town burn the skins of his cows when he slaughters them for market? These are different moral systems as they interact with the predominantly Christian Anglospheres' normal morals. Some are simple oddities, while others start up camp-fire tales and scared mobs. These are the interactions a serious Path Player is looking for, and what the ST has to anticipate (even for an NPC). These are what make paths WORK on the interaction level.
So, for a player, what does a path need? It needs to be inherently different from humanity. Even if it aligns closely, there is a basic difference in following a path and maintaining humanity. Lets look at the Via Caeli vice the Via Humanitatis. In a Christian culture, at face value there does not seem to be a large difference. Follow the rules of G-d versus be a good person. But lets look at the driving motivation: a Cainite on the path of humanity is doing so either to maintain his tenuous connection to the human world or to suppress the beast. Whereas the Kindred along the Rod of Heaven put their deity and his edicts above their own existence (highest ratings). A high rating (9 or even 10) Faithful would see nothing wrong with torturing an accused witch or heathen to get her to confess, and thereby have a chance of saving her soul, whereas a Prodigal would need to make a humanity roll at ratings as low as 1. Now even the most blind see the difference. A path needs to be deeply different from humanity. This difference needs to be seen at almost every session. Otherwise it's just Humanity with a quirk.
The path also needs to be playable (at least at normal Road Ratings). Some paths simply don't work for player characters (here's looking at you, Scorched Heart), normally due the fact that the players are human, and the path is simply too alien, or innately un-human. Others are too one-sided (Honorable Accord) and while perfectly playable for a short chronicle, will quickly become boring for the player and normal to the coterie, thereby defeating the reason a player chose not to use Humanity. Few STs expect any road or path to be played well at ratings outside the 4-8 range. Below that they frenzy too easily and the character has no moral compass to speak of, above that they are caricatures of their road, too single-faced for the character to function through a long chronicle. Not saying it can't be done, but that it takes effort (and then those exceptional road ratings should be central to the characters concept from creation)
Now from the characters viewpoint. First of all, what is a Road?
In the simplest terms, a Road combats Frenzy. A road serves to allow a character to live with her Beast. It is a philosophical, moral, quasi-religion to which the character ascribes to allow her to deal with one of the most basic facts of being a vampire. There are three basic types: Suppress the Beast, Control the Beast, Replace the Beast.
Suppress the Beast: Via Humanitatis Via Regalis, et al. Conscience and Self Control. By following these rules (in your mind as well) you can resist the Beast and (un)live (un)life almost as you did before. But it always there. Fight it. The philosophically simplest of them all. Fairly easy to play well, as they make sense to the human mind.
Control the Beast: Via Beastiae, Path of Cathari, et al. Instinct. Live with the Beast. Change it, manipulate it. If you always interact with it, when it needs to do something it will not be so different from what you normally do, just an extreme version of it. Some follow the idea that by appeasing the Beast normally, it won't fight as much. Some seek to change fundamental points of the Beast (make the Beast more human). Some seem to merge parts of the Beast into their own moral system (Path of Orion, Road of Desire). Fairly easy to play shortterm, but become hard to conceptualize as you explore more of it. (A question I asked back when it first came out is "What's the difference between humanity 0 and Path of the Hunter 10? " Matured some since then, but the question is still valid.)
Replace the Beast: Via Ossium Path of Typhon, et al. Conviction. The most intellectual of them all. Most of these technically fall into the 'Suppress the Beast' category, but they do so in a fundamentally different way. In Replace the Beast paths, the follower finds a concept and ascribes his existence to it. By devoting yourself to something higher, you can ignore the Beast. The path becomes an obsession. These tend to be the hardest for long term play, as it is difficult to explain how they work. By devoting yourself to G-d, or perfection, or knowledge, it become easier to fight the Beast.
Why does a character choose a road? Why does the 'natural' path of humanity not work? For Shovelheads, their humanity is actually intentionally stripped of them. Any who cannot find another path with die, quickly and finally. Other than that though, why not stick with humanity?
For characters with the Mentor background around 3 dots, they could have been specifically trained that way. They may not know that they are different. They may simply see humanity followers as those not as well versed in fighting the beast, or proper manners. Otherwise, they are taught a specific way to combat that persistent desire to glut and destroy that sleeps in their heart.
Other than these, however, it is an intentional choice, and a hard-driven quest, to acquire a road. It involves fundamental changes to the characters psyche, goals and motivations. Why does a character do this? Are they that afraid of the Beast? Do they think that the Beast is a demon possessing them? Are they too old that they find it difficult to consider kine as anything other that meals, so they need something else to control the Beast? Do they have no desire to be human, but simply seek to live at peace with their vampiric nature? Did they almost follow a path before the embrace? Was their conviction for something strong enough to both survive the Embrace and remain a defining feature of their mental state? Are they a great methuselah doing this as an experiment?
What does a road do for a character? It fights the Beast, or it allows you to live with your Beast, or it gives you something to strive for in unlife.
There are really only two basic reasons a character chooses a path: To find a way to live with/despite the Beast, or to do something with their unlife. The question is, why did the character make Whichever decision they did?
Back to the basic question, what does a path need?
It needs to be different, it needs to be playable, it needs to combat frenzy, it needs a story.
How Roads fail is they miss one of these four points, when applied to a specific character.
If it is not fundamentally different, why not follow Humanity? extra rules for no gain.
If it is not playable (probably the hardest one to predict, as it will change case by case) it will result in a character becoming marginalized and ignored, or always being center-stage and the chronicle becoming his story, not the coteries. Either way is harmful to a good game.
If it does not combat frenzy, then it does nothing.
If it has no story (as applied to the character, no one really cares about how or why Ennoia created the Road of the Beast, or that the creator of the Path of Orion is still actively teaching the path to new Shovelheads), then it will have flaws and holes the player is not ready to confront. This can either stop a session in its tracks, or lead to fishmalks and Jamie-Sues as the player struggles to come up with actions that fit all three of the character, the player, and the road.
EDIT: hmm, I should probably mention somewhere in here that the best played paths (PC of NPC) do not make a character a monster, but rather alien. Monsters are low Path rating Kindred. Creatures normal humans need only fear at physical levels. High Road Ratings make us question if the follower was every like us. These are the ones that make Interpol profilers smash their heads into their desks, and inspire Lifetime Specials. They no longer function as we expect humans to, but they still CLEARLY function. If a path is scary, it should be scary not because of what it allows, but rather what if forbids. A follower of the path of Metamorphosis is no longer allowed to have compassion. They cannot see your pain as relevant to anything. And that scares you, it keeps you up at night not because of what they can do to you, but they don't see anything wrong with it, and in fact think it is the right thing to do. The true terror of a scary path is that others think the same way, and you can't comprehend how they changed from normal humans into these . . . things. Even the followers of the 'good' paths do, are even REQUIRED to do, things that normal people can't understand, may even find monstrous.
EDIT2: added the word "not" to make the first 'player' paragraph make sense. D'oh.
Random joking thought: how do Kosher regulations apply to Kindred? do you have to watch your meal for a hour beforehand, to insure you get Kosher blood?
The above is aimless rambling in an attempt to better the game. Not hard and fast rules. Take as you will. Any meaningful addition or argument is gleefully welcomed.