Roboto is the official type family used for Android. The font comes in several weights but the one Google has gone with is slightly lighter than what users may be used to compared to the Arial font. This will surely lead to some complaints about it being harder to read, but I think it looks fine, and going for consistency across platforms is logical.
The company previously tested the change with a small group of users, so they at least have data to back up their decision.
Have you noticed the new font? What do you think about it?