A simple and easy to use amp and cabinet simulator, quite lite on CPU and RAM.
Imterface - pretty self explanatory. If you used a guitar amp in your life, you'll find your way easy through controls.
Usability - from jazz to blues, pop, rock or metal, you'll find easy to get your tone. Of course, it's less tweakable that an amp suite with tons of heads, speakers, mic placements...etc, but as a real amp, you can tweak it enough to fit to your needs.
Sound - pretty good out of the box, maybe a bit thin on the clean channel.
For a freebie is amazingly good. It used to be my main guitar tool for several years.