Tony Romo is one of the best QBs I have ever seen play the game and I have seen them all since the early 60s. He may not turn out to be the greatest QB ever (I hope he does) but he is the best at what counts the most.
His qualities include:
Pocket presence - His awareness in the pocket is uncanny and he avoids the pass rush without ever taking his eyes off the receivers downfield. His ability to step up or slide out of the pocket to avoid the rush is the best I've ever seen, even better than Marino's which I have always considered to be the best ever.
Tom Brady is the only QB that has comparable pocket presence. His is slightly more advanced than Romo as of right now.
Quick release - Again, his release is comparable to Marino's which has always been considered to quickest. He just gets the ball out before the defenders can get to him.
His normal throwing motion is not as fast as Marino's, but he does have a Marino release in his arsenal that he brings out on occasion. For ex: in the Packers game he was being rushed by Kampman in the 4th quarter, and he threw it 2x as fast as his normal motion, to avoid getting sacked.
Reading the defense/ going through his progressions - Romo is excellent at reading the defense and finding the open man. Many times he will go through his 3rd or 4th read before getting the ball out to an open man. All this before the pass rush can get to him.
He is very good at reading defenses. Very rarely do you see him just misread a coverage and get picked off. Most of his INT's come on bad throws/forcing the ball in tight spots.
Accuracy - Considering his free style of play and the angles he throws from at times he has excellent accuracy. Not Troy Aikman accuracy but very, very good.
He has outstanding accuracy, but he is not at the level of Brady or Manning because he is not nearly as consistent as those two, in terms of putting the ball exactly where it needs to be.
Ability to make plays on the move - He is currently the best in the league at making plays on the move. When he gets outside the pocket he is extremely dangerous as he will find someone open and get the ball to him.
No question he is the king at throwing while on the move in the National Football League. Jay Cutler has a better qb rating outside the pocket, but he does not have the same feel that Romo has. Big Ben is a good one also.
Leadership - The players like and respect Romo. They follow him because they know he is a winner and will do whatever it takes to win the game. Staubach had that same ability and we pulled out a lot of games because of it. Even Owens defers to Romo because he respects him as a leader and a winner. Even after going through a tough stretch at the end of last season the players never lost their trust in Romo. That speaks volumes!
His intangibles are off the charts, as Gil Brandt said.
Lots of QBs are 6'5" and have rocket arms, a perfect throwing motion, and were 1st round draft picks but none of them are as good as Tony Romo. Not Carson Palmer, not Ben Roethlisberger, none of them. The measureables that the scouts look for are NOT what makes a great QB. It is the intangibles that, when you add them together, come out with a guy who has it all. Romo & Brady are those type of guys.
Unitas was a late round draft pick (9th round) who was considered too skinny and frail for the NFL. Staubach (10th round) was a great college QB but was considered an inaccurate scrambler and a risk after missing 4 years. Montana (late 3rd round) was a weak-armed guy who was too frail.
On the other hand guys like George Shaw, Gary Glick, King Hill, Randy Duncan, George Izo, Terry Baker, Pete Beathard Steve Spurrier, Jerry Tagge, Steve Pisarkiewicz, Jack Thompson, Marc Wilson, Art Schlichter, Steve Walsh, David Klingler, Heath Shuler, and Tim Couch were all taken as the top QBs of their draft class yet did next to nothing in the NFL. They were all considered by the scouts as the next great QB but they all failed miserably. Many other highly touted QBs had less than stellar careers.
I guess it is because it is so difficult to measure the intangibles, particularly when comparing the college game to the NFL, that there are so many misses. I am just glad that, even though we had to wait 3+ years to see him play, Tony Romo is a Dallas Cowboy! The guys has it all and will continue to break records for a long time to come.