John Petrucci of Dream Theater. He's been called the best metal guitarist, even though Dream Theater is more harder prog rock than metal (only a few really awesome heavy metal style songs). Alex Skolnick of Testament is a beast on guitar (also played with the Trans-Siberan Orchestra, another band, and has his own jazz band). Another awesome guitarist is Dan Donnagen of Disturbed (no clue if I spelt his last name right), which despite being called a metal band, is more of a hard rock band. Note that metal is a branch of rock (in a sense). Metal guitarists have to be far more skilled than most because a lot of metal takes major skill to play. Just look at Dream Theater, they're an example of just how crazy Progressive Metal is (think of Rush, just a lot heavier).