For various reasons, including a poignant fear of rabid addiction, I've largely stayed away from MMOs. Not even World of Warcraft has been able to lure me into massive multiplayer worlds, but I have to admit that I'm more intrigued by Lego Universe than any other MMO that has come before it. Ok, so I'm a sucker for Lego.
My enthusiasm for a multiplayer world littered with bricks was just tempered by Rock, Paper, Shotgun's review of the game, though. According to the author, the game has numerous issues, including clunky vehicle and building controls, poor pet AI, and an auto-aim mechanism that makes lousy choices about what to target. The game world also appears to be rather barren when it comes to both content and other players to join one's escapades.
That said, the reviewer sees potential if the game can grow to match what's available with other MMO experiences. He also applauds the fact that Lego Universe seems to be a safe place to unleash kids; the developers have gone to great lengths to ensure that potentially objectionable names or creations are vetted by actual people before they're given final approval. Perhaps most importantly, the game is said to have a "very deep understanding of the fun and mythos of Lego," which at least bodes well for the future if the other issues can be ironed out.