For an app, its surprisingly satisfying for a real guitarist to play (when no real guitar is within reach), and its sound, although far from a perfect replica of a real guitar, is quite convincing at times.
But listen to me, buy the in-app purchase stuff, especially the 4play thing! It allows you to route any of the guitar notes, bass notes, and chords (like a pad) to either the Guitarism virtual guitar sound, or any virtual MIDI channel. I highly recommend Arturia iSem for the bass notes, DXi for the chords, and the guitar notes through the internal Guitarism virtual guitar sound. With the virtual analog synths playing the bass notes and chords alongside a very convincing virtual guitar sound, its very... old school prog rock.
Wanna get really fancy? Open Guitarism in Audiobus as an input along with the two aforementioned apps. Put the awesome delay effect Crystalline in the Audiobuss effect slot, and then just use the speaker or your favorite Audiobus recorder as the Audiobus output. 21st Century prog!
Guitarot about Guitarism - Pocket Guitar