GW2 dynamic events, as I understand it, are vastly different from Rifts. In fact there are more differences than similarities that I find it hard to compare. The only thing that is really similar about Dynamic Events and Rifts are the fact that you can do them in groups.
If I understand it correctly GW2 quests = dynamic events. So some people think that the big dragon you fight is the only kind of DE but if I understand it correctly there are large scale DE's and solo DE's. From just reading the webpage everything in the game is a DE. So think of it this way, you don't have quests anymore in GW2 you only have DEs which come in all sizes and chain in different ways and change depending on the environment or what someone may have come by previously and done.
Also DE's change as the player interacts with it or chooses not to interact with it. For example if players choose not to fight the enemy they start taking over the land and building fortifications and sending out assault squads, snipers etc to attack near by towns.
Quote from GW2 webpage about DEs.
So the list of things a DE shares with Rifts are:"A single player decision can cascade across a zone, changing the direction of a chain of events until they dramatically alter the content played by players in a map."
1) You can do them with a group except in GW2 I don't think you need to form one. Also a level 50 can't power you through as all level 50's would be normalized down to max level of the zone.
2) You can gain XP off of them and loot/gold I believe.
3) They both aren't part of the linear quest line... But GW2 doesn't have a linear quest line.