It's worth noting now that this review will be conducted from the standpoint of a developer. That is, I'm targeting this review of Sandvox at someone who knows how to code, but wants a rapid design tool to use since, naturally, it's extremely tedious to code all the HTML by hand - especially if all you want is a demo site for a client or just to try stuff out.
From this standpoint, Sandvox feels very much like a glorified iWeb. You must choose a theme (which includes a pseudo-blank theme) and you cannot really edit or modify how that theme feels, unless you feel like creating your own package and learning how Sandvox reads templates. Although you're welcome to add your own custom HTML, you can only do so within the confines of the theme you're using. Put a different way, if you don't like the theme you're using, you'll have to buy one from their site and if you don't like those, then you're SOL.
Fortunately, however, Sandvox includes a truly impressive set of themes, so the average person is more likely than not to find something that they like and most, if not all, can be customized with a corporate logo or something of that sort. In addition, all themes seem to render excellently on the standard browsers, which should suppress worries about cross platform compatibility. So, while it is a more powerful iWeb, there is a decent amount of flexibility that those who are looking to design a site rapidly will enjoy.