Aaron Rodgers thinks Matt Flynn will be a "top-15″ quarterback | ProFootballTalk. He's speaking with a little bit of bias because they're good friends, but I don't think he's wrong: "the team that's going to get Matt is going to be very happy."
But what is a Top 15 quarterback? It's not being named as an All-Pro or Pro Bowler, though he could be that good, at least for a season or two. Below that is a number of quarterbacks who should be starters (players like Jay Cutler and Matt Ryan) and I could see Flynn falling into that group.
Top 15 could imply average since there are around 32 teams. But I don't like to label quarterbacks as average. Are they good enough to win a championship? Quarterback isn't a position you fill with a stop-gap, and no long-term plan. And Flynn isn't someone who's just good enough. He won't do it all by himself, but he's good enough to win a championship.