A player can solo URU with no need to group, which sometimes makes URU feel more like a really pretty chat room then an MMO.
There's very little in-game guidance - a hallmark of the Myst franchise, there's a lot of "run around and click on everything until something opens" happening. Which can be frustrating, as the camera can stick and leave you staring at a blue sky while you run off a cliff (note: First person PoV is the only way to control the camera easily).
We spent a lot of time wondering: Well, we found that bit, and ran over there and got that other bit and now we're here... So, why did we just do all that? And getting no response.
And getting no response seems to be a chronic problem. While we hope that URU picks up support and gains a flourishing online community, at the moment there are times where we wondered if we had actually logged on or if we had clicked the single player version by mistake.