Although personally I think the rifts are pretty cool. I am not sure who else did them and on what scale but they are definitely a change of pace from other things I have seen.
I know Warhammer did it before Rift; they were called Public Quests. I think Warhammer did originate the idea, but I am not fully certain. Regardless, it was a great idea then, and is a great idea now.
While there are definitely similarities between Rifts and PQs, I am considering Rifts and the invasion technology something new in the MMO world, and something that I think is a great addition to the landscape.
PQs and Rifts are both scripted, and they both give you rewards based on your contribution to taking down the enemies if you are grouped or not. Both PQs and Rifts encourage random people in the area to group up for better rewards and better chance of success. However, PQs were in a set location and ran through a set script. Once you beat it once you had a good idea on how to beat it again. Don't get me wrong, they are a lot of fun, and a great idea which is at the basis of Rifts and invasions.
Where Rifts and invasions really bring something new is their ability to spawn in random places and at random times. This may not seem like a lot, but I wouldn't be surprised if there is a lot of tech behind the rifts and invasions, and it really does change the feel of the game a lot. After playing Beta1 I've really been hooked and had a problem going back to play any other MMO.
Back on topic: Yah, I'm hooked. I've been hooked. I preordered on 12/28 when Amazon first started accepting preorders :)