He's also an excellent returner, but I agree that his receiving production has been very mediocre. He is also overrated as a deep threat, averaging 11.8 y/c for his career.
http://espn.go.com/nfl/statistics/player/_/stat/receiving/sort/yardsPerReception
That's very poor considering how many 1,000 yard-receivers averaged significantly more per catch. Look at Vincent Jackson's numbers (1,384 yards, 8 TDs, 19.2 yards per catch).