Former MLB player, Aaron Guiel who once played for Kansas City and the New York Yankees had faced Darvish in the Nippon Professional Baseball a few times. According to Guiel, Darvish is like a Pedro Martinez:
“They don’t look anything alike, maybe zero physical similarities, but Darvish’s pitches and pitch sequences resemble Pedro because of the blend of power and finesse,”
" ...Martinez was often accused during of being a head-hunter. Darvish, 25, has that quality too, according to Guiel. ...He has an edge to him..."
"Guiel ... figures Darvish would rank among the top 10 pitchers he’s ever faced. With the Royals and the Yanks, he faced Cy Young Award winners Johan Santana, Roger Clemens, CC Sabathia, Roy Halladay, Randy Johnson, Barry Zito, Chris Carpenter, Pat Hentgen and Cliff Lee."
http://www.lfpress.com/sports/baseba.../19140911.html