This is a walkman worthy of the name and a great alternative to an ipod.
The first thing you notice is the size, its both thin and small and nice to hold in the palm of your hand. The next thing is the top quality screen, photos look vibrant on this player. I don't use it much for viewing but what I've seen shows that Mp4's / video looks crisp and realistic.
The most important part is the music and on this Sony does not disappoint. The sound is among the best quality available on today's MP3 / MP4 market - with a good set of headphones you will hear sounds in songs you didn't know were there. There are also Sony's options on the graphic equaliser to modify the music. The sound really is first class.

The intitial menu system is easy to navigate although the submenus could be a little easier, but you get used to it pretty quickly and if you buy a quality walkman you would expect many options. You can also choose background / icon colours to personalise the player.
It is true that as there is no switch on / off button (however, pressing and holding the option button switches the walkman off) you might occasionally leave the walkman on, only to have the battery run out sooner. But it is also true that one charge can last upto 5 days with occaional use. There is also the hold button that you can use to ensure that the player doesn't switch on in your pocket.

The NW7S638F is a top quality, stylish MP3 and if you are considering an alternative to an ipod this walkman deserves your attention.