To answer the question the thread poses, I think yes, he is a legitimate quality NFL starting quarterback.
As football is a different sport than basketball, I'm sure he much prefers starting to being a role player. Backups in the NFL don't get reps like they do in the NBA, but that's really neither here nor there...
He seems like the Kyle Orton-style stop-gap quarterback. Which is to say he's a better starter than whatever other options are on his team, as well as a better fit for many of the teams in the league than what they already have, but they should look to find an eventual replacement if they want a real catalyst for success.
I think he's intelligent and mobile, but I don't think he's elite or anything like that. He's a capable starter, but I don't think he's a franchise quarterback. He may develop into one, but he is not right now.
Right now, we're talking about this after he's played two 'lights-out' games against two AFC West teams with extremely porous secondaries. KC just lost their all-star safety, Oakland's star cornerback is playing for Philly.
This will be easier to analyze farther down the road, once he's played higher caliber football teams. If he's still performing like this at the halfway point of the season, perhaps we can anoint him Buffalo's savior. More likely if he gets the Bills deep into the playoffs.
The last three years, as completing 60%+ of your passes has become standard, he hasn't done it. In 2008 with Cincy, he threw for eight touchdowns and nine interceptions. In 2009 with Buffalo, he threw for nine touchdowns and ten interceptions. So far this year he's completed 45 of 71 passes (63.4%) with seven touchdowns and only one interception, but it's been against teams with bad secondaries. We'll see, I guess.