I can't think of a single game that manages to have enemies correspond to your level rather than area or story progression actually contribute to the game. It just makes trying to get better gear ultimately a pointless task because the enemies get strong at the same rate so you might as well stay weak.
I think it worked really well in Rift because there were world events that happened everywhere, which were really fun, so high level players could participate no matter what zone they were in but wouldn't ruin it for low level players, and it also allowed them to help their lower level friends in questing.