I've tried Metaverse, and a few others in their betas and from what I've seen most of the other platforms lack the customization that SL has. Metaverse doesn't even have a build mode, all content must be created outside then uploaded. Their sims can support 1000 users but only with 9 different non customizable avatars to choose from. Imagine newbie island, only thats the entire world. Users might flock to the new big thing at the on-set but I know they'll lose interest fast, and I'd be willing to bet some might find their way to second life where they can dress how they want and buy cool stuff in world instead of being herded like sheep in the metaverse.