The game has a bit of a learning curve. It has the most god-awfully clunky chat system I've ever seen. It quite literally took me 30 minutes of digging through FAQs to figure out how to add the guy who invited me to my buddy list, and how we could send tells back and forth. The tricky bit is that you have no buddy list and cannot send tells at all until you get something called a KI in a completely separate zone from where you start. It also does not support WASD movement. It's mouse movement or arrow keys, your choice. Joining someone to hang out or solve puzzles together involves using a machine that looks like a mailbox, and that you also have no way of knowing how to find when you start. Other oddities await. All that said, if you can weather an hour or so of frustration, a truly unique MMO experience awaits.
First off, the game is gorgeous. You wouldn't know that at first because the default GFX settings are what an average PC could have handled 5 years ago (or whenever this first game out). Spend some time fiddling with the settings to max them out, and beautiful alien vistas await:


The game also has technical innovations I haven't seen elsewhere, which is very impressive for such an old MMO. For example, voice chat. When you enable it, the volume at which other players hear your voice is determined by how close together or far apart you are. There aren't really chat "channels," you need to be in the same room to hear each other. There is also a setting to make your voice sound the way it would in your current environment. For example, if you are in a corridor with stone walls, your voice will echo slightly.
Another thing that amazed me was that you can actually affect the world in small ways. There are objects that you can move around. They stay where you leave them from session to session. Machines that you turn on or off also stay the way you set them. The the game handles the inconsistency of different player experiences by splitting off the game into shards. Each shard can hold up to 50 players, and is tuned to the player that started it unless they decide to open it out to more players (not exactly sure how that works yet...there's that learning curve again). However if you go to someone's shard and change something, it will remain until someone else alters it. Very neat.
Finally, if for no other reason, the game gets credit from me for being such an enormous departure from typical MMOs. There are no classes, levels, loot, or combat. Mainly, you explore and solve puzzles. The more puzzles you solve, the more content you have access too, and the more of the back-story unfolds. You start with a little hut on a floating island:

As you solve puzzles in various places, your island evolves. Books are also added to a shelf inside your hut:
These books can be used to travel to areas you have unlocked:
That's it, that's all there is to do. Explore, socialize, solve puzzles, and collect books. And I think that's awesome.
URU is like nothing else I've played, and quite refreshing for it. At 100% free, it's also hard to argue it isn't a good value. If you do find yourself in the mood for something well and truly different from most MMOs, I'd say URU is well worth a spin. However, if you do decide to take the plunge, for the love of all that is holy read this FAQ first and save yourself some suffering.
In other news: CO is reactivating lapsed accounts for free this weekend, LoTRO just launched the spring festival, and I'm still obsessing on Allods Online. I need more spare time.