UPDATE: See my post on MESSENGERs second flyby.
This is only the second space vehicle to visit Mercury. Last time was over 30 years age in 1974 and 1975 by Mariner 10.
The images under are from the Messenger web site.
Notice the double walled crater.
Mercury is completely covered in craters. Any new craters will erase older craters leaving the crater density unchanged.
The ray pattern from the bright crater in the top left is a familiar sight. The Moon has similar rays. They are caused by the ejection of matter from an impact crater.
Credit for these wonderful images belongs to NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.