Who needs eyeballs, I have measurments!
One immediate advantage of a 30MP 645 sensor vs a 20something MP 35mm "full frame" sensor is pixel pitch. The individual sensors on the sensor will be larger, and much more resistant to producing chromatic noise. 35mm DSLRs get around this by applying in-camera noise reduction. Recently, Nikon has become rather good at this (at least on the D3 and D700). That said, it's better still not have to apply noise reduction at all.
The above diagram gives a relative idea of the sensor size of different formats. The 645 sensor is both bigger and more rectangular than the Kodak.
EDIT: This chart, from those nuts at RED: