The interface is pretty easy to get around, especially after watching the Tutorial demonstration. Pointing your cursor over the Loop Browser at the bottom of the screen will pull up a menu where you'll find hundreds of loops for use. Grabbing clips over to the main editing panel is easy as holding the A Button and dragging it over. With a press of the B Button though, you can preview the loop before inserting it into the main area. The volume settings on each clip can be adjusted, and when you need to see if things work well or not, you have the ability to isolate or mute entire rows.
The library of loops available is quite extensive, spread out across three main categories: Dance, Hip Hop and Techno. In each of these are several sub-sets consisting of different types of loops such as Bass, Synth and Sound Effects. In order to gain access to additional loops, you'll need to connect to the Loop Shop. Through Nintendo Wi-Fi Connection (Pay & Play), you can download loop packs from such genres as Latin, Pop, Rock, Old School, and more. Packs range in price from 200 to 500 Wii Points a piece. Whether you'll see them as worthwhile investments or not will likely depend on how devoted you are to the entire application.
So far, it's shaping up quite nicely, and I have a sense of optimism towards this title's potential success. You can expect a full review of this title soon. In the meantime, check out WiiloveitTV for some videos of Mix Superstar.