As it's name implies, the D300s looks, feels, and operates almost identically to the D300. There are a few differences in the controls on the back and the card slot cover, but otherwise it's the same chassis.
That makes it a bit bigger and heavier than the competition, but it's still quite comfortable to grip and shoot with. One of my few complaints about the body is the proximity of the front dial to the rubberized grip; I find there's excessive, uncomfortable friction when using the dial because of it.
The release mode dial provides access to the various shooting modes--single, low-, or high-speed continuous, Live View, self-timer, and mirror lock-up. New to the D300s is a Quiet shutter release mode that slows the mirror flip to dampen the sound and overrides the focus beep.
To make room for the Live View and Info buttons, Nikon discarded the latch for the card slot cover; now it uses the more common slide-and-flip-up cover.
I don't really like the feel of the multiselector, which hasn't changed since the D300; it's a bit mushy and a little to easy to accidentally press the button. On the other hand, the dedicated switches for the autofocus mode selector and metering are very convenient.
The buttons down the left side of the camera remain pretty much the same as the D300, but the slightly raised sides around them are gone. Now they feel flatter and more difficult to differentiate by touch.
The interface for working with movies is somewhat annoying, with too much reliance on the menus and too many button presses required for some activities. For instance, because the playback button controls volume and brightness, in order to review photos and movies shot while in Live View mode you have to first exit the mode.