Then Nikon also gets the nod for really low light work although coupling the Olympus to the fabulous Voigtlander 25mm f/0.95 or even the new Olympus 12mm f/2 and Olympus 45mm f/1.8 lenses, combined with the lovely OLED display and convenient manual focus controls (particularly with the Olympus 12mm lens), the Olympus is a joy to use.
Overall, the Nikon still wins on image quality and generally less work is required during post processing. The Olympus is definitely the fun camera.
Over the past week I have used both cameras in similar circumstances, and here are some of the results.
Olympus E-P3 and Olympus 12mm f/2
And now for one from the Nikon D90 and Nikkor 10-24mm zoom
Of course it is a bit unfair to compare any of these images as the lighting was quite different in each and there are evening and morning shots too.
Despite the camera and the lens, if you know the limitations of your kit, you can work to get great results. Obviously some things can be more difficult with some combinations of camera and lens but that is where your imagination can take over.