It is released today, so I guess I can comment on it. I have not played it in the past month or two, so maybe they changed a lot (I doubt it).
The game is quite colorful and has some very nice environments to play in. The combat / loot system is also somewhat interesting as in the combat is very action based, not at all turned based MMO combat. Basically bad-guys are running around and you need to attack them in a manner similar to a FPS. If that is with a sword then you get in there and dodge and swing your sword. Loot pops out of each mob which is generally health, armor, and mana (imagination orbs, the magic of Lego online). Sometimes special stuff will drop, but that is very rare.
Many areas are gated by certain mechanisms. For example to climb up to some platform, you might need to quick-build some object that requires 10 mana. Until your mana pool is big enough, you simply can not go to said area. Another gating mechanism is that you need to use some specific object (gained by questing) on other objects.
Quick-building: There are piles of legos in the world that can turn into specific objects, like a bridge, ladder, etc… They are in fixed positions and can be used by anyone for a short period of time after they are built.
Leveling Up: There are not really levels, but simply equipment levels that you need to buy with faction tokens. Faction tokens are dropped from any mob, although they are very rare to drop from anything other then very tough mobs. Even the tough mobs are unlikely to drop these tokens.
Faction Tokens: You need a lot of them. 100s, if not 1000s for a single equipment piece.
Needless to say, Lego is very, very, very grindy game. It is neat to explore at first, but once you have done that, the only thing left to do is grind. Killing the same mobs over and over for hours to get faction tokens.
The chat system: This must be mentioned since it is uber-filtered chat. There is an allowed word list, opposed to a disallowed word list. This posed tremendous problems as in many in-game words were not in the dictionary. You might want to ask, “How do I get to Gunslinger wall?”, but Gunslinger isn’t in the chat interface, nor is Gun nor is slinger. Also if you are not such a good speller, you are SOL. The forums are even more 1984.
If you are a you kid, who likes repetitive game-play, then this is the game for you. Otherwise, stay clear.