Although I can just about play the guitar, I could never read music. I was always from the Sex Pistols school of thought that knowing how to read music or play and instrument properly wasn't really important to be a musician.
Overture is for all those that believe otherwise, enabling anyone that knows how to write professional looking musical sheets and scores. Adding and removing notes is as easy as drag-and-drop and you can even record your masterpiece into a MIDI file to get an idea of how it would sound. The aim is to put as many essential composition components at your fingertips so that you spend more time composing and less time scrolling through menus for the right note.
Most professional musicians either use Overture, Sibelius, Finale or Encore as their notation program of choice which gives an idea of the esteem that Overture is held in. If Overture has an advantage over the above however, it's probably that it's incredibly well presented and elegant in look and feel. Added to this, it's considerably more user friendly than most other major packages allowing beginners to get their first taste of music composition. Just try composing one note in Finale or Sibelius and you'll see what I'm talking about.
One of the biggest joys with Overture is the ability to add and edit lyrics with relative ease. For most users, this means that Overture will be their immediate choice ahead of those such as Sibelius that don't even support such a feature although professional conductors complain that Overture does not allow intricate control over notation that you get in other packages.
If you're looking for a balance between ease of use and professional results, then Overture treads the balance perfectly.