I think that without some side lighting the best way to coax some texture out of this would be in post processing, which you haven't done any of (Are you shooting in jpeg?) Some enhancement of the micro-contrast should help. This has various names depending what image processing program you use, but usually it's called clarity, definition, or presence, or something similar.

Although as Marko says, the bright spots from the onboard flash don't help and will kill the mood slightly.