Many guitarists (and other instrumentalists) are guilty of playing way too many notes when taking a lead or solo. Even experienced musicians are guilty of this. The problem with playing a lot of notes for a long time is that the notes no longer have meaning, purpose, and interest. To the person playing, it might seem really cool to play a lot of notes for a long time, but to the listener, it gets boring, monotonous, and sometimes downright irritating.
The key to avoiding this is to treat your solo like a conversation. You want to leave space to breath. In conversation, no one talked without taking a breath or pausing periodically. Leaving space in your solo actually makes the notes you play more meaningful (assuming you know what you’re doing!). A well placed moment of silence in the midst of a solo can add huge impact, emotion, and lift the solo to a higher plain. Why? Silence makes the listener unconsciously pay closer attention to what you’re doing and makes them beg to hear what’s coming next, especially when the notes are chosen carefully and purposefully.
For a great example of a musician who used silence well, check out the album Kind of Blue by Miles Davis. It’s an album every musician should own and know thoroughly.
