There were two big design elements that attracted me to Rift originally: the make-your-own-class system and the Rifts-and-Invasions dynamic content. I'm a big fan of dynamic content. I would like nothing more for MMORPGs to do away with "quest grinding leveling" and "end game raiding" and just have one continuous dynamic playfield. Rifts and invasions didn't quite live up to that... but Instant Adventure takes MMORPG design one step closer to fulfilling that dream.
The premise is simple: a new UI element lets you click "join now" to join an Instant Adventure team. There can be several going on at once, but currently they're limited to two high-level zones, Shimmersand and Stillmoor, and only available to players level 45+. But no matter where you are you can join, get teleported right to where you need to be, and start participating.
The Instant Adventure quests themselves lead you around the zone, killing monsters, interacting with the environment, and completing a number of quests that are actually quite interesting. For example, you might find yourself defending a fortress in Stillmoor against a flood of hundreds of undead skeletons, armed with temporary bombs to blast them away as you deal with a few larger abominations. With wardstone defense and boss fights tossed into the mix, Instant Adventure has a pretty good variety of elements to throw at players.
I have three complaints:
No rifts as part of IA, nor does IA ever encourage you to close rifts currently in the game world.
IA doesn't switch over to a zone invasion, so if there's a big exciting dynamic content invasion going on, it doesn't tell you to go do that instead of the current IA objective.
It's 45+ instead of 1+.
Still, it's a good step in the right direction and I hope to see Trion expand upon this formula further, especially in Ember Isle!