I have stayed at all the lodges at the Grand Canyon (both North Rim and South Rim) and I would have to say that staying at the North Rim Lodge in summer is definitely THE BEST.
As others have noted, the north rim has only the one lodge and so it is MUCH less crowded than the south rim (which is a zoo in summer). Because the North Rim is at a higher elevation (7-8000 feet), it is also much cooler than the South Rim with pine trees, etc. Note: the highlight of the North Rim is the peace, quiet and serenity. The South Rim has more cafes, shops, historic buildings, the IMAX theater and other 'attractions' which some people prefer depending on your tastes.
As for the lodge itself... it was built in the 1930s in the grand National Park style with fancy stone and woodwork. It sits right on the very edge of the canyon with two huge patios looking out over an incredible view. Getting a glass of wine, kicking back in one of the old wooden chairs and taking in a sunset there is a prime canyon experience. The dining hall (with its high ceiling and incredible views has good food at reasonable prices - make reservations).
As for the rooms - there are no rooms in the main lodge building itself. You can either stay in little stone or wood cabins (highly recommend) or in a block of more modern hotel-like rooms. Both are nice and clean, nothing fancy - you will not want to spend much time in the room anyways.
One last note - on your way in, stop at the little Jacob Lakes Lodge (about 45 minutes north of the park lodge) and get some of their homemade cookies - they may be the best on the entire planet.