PvP Rifts within Rift are designed to help centralize PvP in certain areas and to benefit those who take part in PvP there.
This is one push towards benefiting those who take part in PvP, and so far has been a great one.
For anyone not familiar with them, bascially they are a special type of rift that requires you to run Sourcestones from the rift to one of three locations (each rift has its own locations and the one you need to "drop off" the sourcestone at is randomized).
Some of these are further distances than others, which often times forces players to run from one area to another, (presumably) dealing with players of the enemy faction in the process.
As for the locations for these rifts, they are opened at any raid tear within Iron Pine Peak, Shimmersand and Stillmoor.
Up to one PvP rift per zone can be opened at any given time, for a total of three.
The goals of each rift are the same, regardless of the elemental type (fire, water, etc.
) or where it is opened:

• for the attackers there is a main Idol protected by four smaller Idols.
  Their goal is to take down all of these before the defenders get all of their sourcestones returned
• As for the defenders, the goal is to turn in 35 sourcestones

When players are close to a rift, they will get a buff that increases the amount of Favor and Prestige earned.
This is the main facilitator of PvP combat because the rewards make it well worth fighting it out, and continuing the battle until the rift is closed.
The only real downside to this is that it is only up while near the rifts, and is not up while chasing down the sourcestone runners.
For the attackers, extra rewards are gained when returning a sourcestone that a defender drops.
As for the defender, rewards are gained when dropping off the sourcestone (and everyone in the person's raid is also rewarded).
And of course both sides also benefit when killing players of the opposite faction.
The positive points of these rifts include:

• There is a lot of PvP (usually) since they help centralize it
• They reward notoriety with the daily/weekly PvP factions
• They give a meaningfull group-based end-game experience

Now, when it comes to the negative parts of these PvP rifts, they include the following:

• Despite being PvP raids, players can do them without any PvP at all, and still gain Favor and Prestige while closing them.
  Though I strongly feel that PvP rewards should require PvP, there are also dailies that are very similar (in that you use PvE to gain PvP rewards)
• The rifts often end up in mass ganking of one side or the others (which is usually Guardians), destroying the true fun it is meant to bring
• They're all the same - although this is good in the sense that they are easily understood, it also means that they do get a bit repetitive after a while

Overall, I am quite impressed with the rifts in the game and will happily await new additions to them or other unique ideas.
I've been having a lot of fun going from one rift to another, PvP'ing along the way.