Improvising is one of the most fun aspects of guitar playing, for me anyways. Improvising doesn’t have to be soloing, although it could be. It can also include coming up with new chord progressions, throwing licks or guitar riffs in between the chords you’re playing, or coming up with an alternate part to a song.
Improvising on guitar is a broad topic, but I enjoy it most because it really lets me do my own thing with the music – it is that room for creative expression that I think we all want.