As a Roddick fan, I'm going to say it's honestly about even in the grand scheme of things, IMO. (Currently, anyway; he took some monster heat back in the day, I recall.)
I've seen people make the argument that Roddick's a walking example of the 'weak era', that without his serve he wouldn't have made it out of Challengers, that they've seen 4.0's volley better than he does. Hogwash. His records and highlights speak for themselves, and aspiring to have a better career than Andy Roddick is to aspire to great things indeed.
On the other hand, I've also seen people that claim Roddick would have cleaned up the 90's, or that without Fed he would have been an absolute lock for 7+ more majors or some other ludicrous number; also hogwash. He always had weaknesses that were target-able for the top guys, and while I would happily agree that he'd probably win a few more without Roger his absence would not mean that Roddick would automatically jump into the GOAT debate.
Roddick was a excellent player who maximized the talent he got in spite of the fact he was never going to be an all-time great like Sampras or Agassi. He always had exploitable holes in his game no matter what incarnation of him you watched, but his strengths were such that if he played at his best, the racquet would be taken out of his opponent's hands more often than not.