The new Nephalem Rift feature in RoS adds completely randomized dungeons to Diablo 3. In the few that I've done, it seems like each instance of the Rift may have some constants. For example, there seem to always be some kind of power shrine present. So far in every instance, I've found at least one treasure goblin. Also, there seem to be a very large number of elite groups. Do these things occur completely randomly or are there some things that will always be present in a Rift? If so, what are they?
The only constant is that there is guarenteed to be enough monsters to spawn a rift guardian. Though in some there is an overabundance of monsters in others you have to kill almost all of them.
Everything else about the rift is completely random.