A couple things I haven't seen mentioned in this thread yet:
Stereo Speakers
The stereo speaker quality is excellent for a game controller. Sound is crisp and it has a wide volume range. The software smartly adjusts certain music/sound effects coming from the TV based on the GamePad's volume level. With the volume set to high, there's a nice front/back stereo effect that occurs. The only downside is that sometimes the screen / GamePad music and sound isn't synchronized, causing an unwanted reverb due to latency differences. However, I can see this adding a nice ambiance to some games (e.g. an echo effect in a cave).
AC Adapter
A lot of people grumbled about this when they saw it, but what they really were complaining about was the battery life that necessitates the adapter. However, the AC adapter itself is a great feature. It allows you to play long gaming sessions away from the TV using just the GamePad without having to worry about battery life or having to minimize brightness settings. The charging stand makes it even more convenient. And you can play while it's charging, so there's no real downside to having it.