After using a Surface RT for the past week, I can explain it in one sentence:
Its more than an iPad, and less than a PC.
The Windows RT-powered Surface will not replace your desktop PC or your full-strength notebook. It is, instead, an ideal companion device for a Windows PC, with great mobility. It is powerful enough that it alone can handle most work and play duties, even on an extended business trip or vacation.
The hardware itself is drop-dead gorgeous, and the build quality is exceptional. This thing feels good in the hand, and the kickstand works exactly as advertised: propping the device at a 22-degree angle for watching a movie or working with an Office document. It is very thin (a millimeter or two thinner than the third-generation iPad) and very light (a fraction of an ounce heavier than that same iPad, despite having a much larger screen).