I think a lot of this goes to the Cowboys, and to game planning. Our receivers have TONS of separation in that game, and Jay is able to take advantage of it. He does have good throws as well (the short slant throw to Chambers was a thing of beauty), but he had much more to work with than you see in most games.
I'd also suggest looking at the last game vs NY - another solid (though not perfect) game from Jay.
I think he brings a great deal of fire to the team, and has the athletic ability to help the o-line protect him by being mobile enough to get out of trouble.
I think he's a good QB, but has not necessarily had the tools around him. Last year, the 0-line was questionable, and we effectively were lacking a 2nd receiver. Jay still turned in two games that were 'career' games for him.
I think he is good enough to take advantage of things, but needs help from other players. He gets into trouble when he tries to make a big play on his own (or when a player doesn't do his part, witness the INT for TD vs the Jets, which McKnight misplayed that signficantly in my book). finally, he does have injury issues that can limit him.
While I'm eager to see what Feeley can do, I would not be surprised to see Jay try to kick it in gear and make this a tough competition. It may be that Fielder wins early due to his knowledge of the offense and Feeley gets his shot later in the season due to injury. Course, this is the same scenario we discussed last season with Griese, and we all know how that turned out.
Right now, I want the best of the two available to start, and if that's Jay, so be it. If it's AJ - that's fine too. I think AJ should be the preferred winner by the front office (due to the investment in him) while Jay has an edge due to familiarity with the system and players. Should be a good battle.