I like that it gives you an overview over your website's performance from different angles (organic traffic sources).
It is easy to use for smaller businesses or even individuals without too much knowledge about SEO/SEM etcetera - they can get started with just using this tool! As mentioned before their interface needs some work but once used by themselves most people will be fine working within these limitations. They offer several useful insights into what works best when optimizing websites which we have never thought off previously so far.