What do you think of when you hear the word "invasion" in an MMORPG? The first image that comes to my mind is a bunch of NPCs screaming for help, while some foot soldier grunt enemies stand around waiting for you to slaughter them, pick up their loot and move on. The town still is invaded after (perhaps until you hand in your quest), the NPCs still scream, you yawn and go back to collecting rabbit feet or whatever else is in your quest log. Somehow, the terrified quest-giver still wants her rabbit feet while frenzied nasties are destroying her town; which remains intact. Sigh.
Imagine instead you're on your quest to find rabbit feet when you notice something odd. You've been down this path a hundred times, but you don't remember seeing these kinds of trees... and why are there skeletons popping up? What’s with the music changing all of a sudden? And... are those tentacles coming from the sky!? You make like a jack rabbit and run as fast you can back to town, only to find that those skeletons have taken it over and are creating more skeletons to find sacrifices to whatever tentacled beastie is coming out of the hole in the sky. And then they rush at you. Welcome to Rift.