The Galaxy J has the 2.3GHz quad-core Snapdragon 800 processor with 3GB of RAM and those are the only two main changes from the mainstream Galaxy S4. The phone features the same five-inch full-HD Super AMOLED display and the same slimy plastic back.
Since this is a Japanese flagship, the Galaxy J adds a few pounds of weight from the waterproof design. Most Japanese flagships have some water resistant design and it looks like Samsung has worked to make the Galaxy J at least a little water resistant.
The Galaxy J will start on NTT DoCoMo in Japan with three colors, satin white, lapis blue and coral pink, the weird names for colors are back. One thing to note is the Galaxy J has different color home buttons to match the back color, a little odd to our eyes but this may be something common in Japan.
NTT DoCoMo will start selling the Galaxy J on its LTE-A service, starting sometime in October. Samsung is unlikely to bring the Galaxy J to the rest of the world, with the Galaxy S4 still selling pretty well and the new Galaxy S5 on the horizon in a few months.