Do you not get any DRC errors? C4 pin 2 does not look like it has a connection to ground.
Also, I would increase the clearance around your 3V3 and +5V tracks and move them away from any pads. They pass quite close to several pads and could potentially cause shorts if there is any misalignment of the solder mask. Be sure to move any silkscreen off of pads, like the C1, C2, and C5 ref ids.
The 3V3 and GND tracks that run under U2 are probably not necessary.
If you don't want the values rendered on the screen you can turn them off under the "Render" tab.
Although I too would probably add a few vias, especially near U1 and C3, but his board is not quite as bad as it first appears. There are connections between the ground plane and tracks on the top through many of the pin headers.
Edit: I see you are running the crystal signals out to a connector, is this necessary? It's not really a very good idea.