This is a post taken from r/nfl at Reddit; it was stated by a Patriots fan of all fans too!
If you had any doubts, this should shatter them, despite what happened last season. Anyways, this statement below is an amazing read, so here goes:
I think the main 3 things are his advanced throwing mechanics, his advanced mental grasp of the game, and his prototypical NFL quarterback body. Those are the three things that remain as question marks for a lot of the other young quarterbacks in the NFL, and the first 2 things are the most difficult things for quarterbacks to develop.
Tim Tebow isn't an NFL quality quarterback because his throwing mechanic is drawn out which leads to a long delivery and inaccurate passes, by comparison Luck has the kind of throwing motion that is common to elite NFL quarterbacks. Note that some very good quarterbacks have had nontraditional throwing motions in the past, Phillip Rivers comes to mind, but that's a hurdle they have to overcome; Luck will never have any such hurdle.
Luck also clearly understood the mental aspect of football and played in a pro-style offense at Stanford. One of the big question marks surrounding Cam Newton when he came into the league was whether he could adapt to NFL-style play calling since he didn't run traditional plays at Auburn. Although Luck threw a lot of interceptions last year, and that relates to the mental aspect of football, that's something that can be corrected through coaching. And if a smart kid's worst problem is a coachable problem, it won't be a problem for long.
Finally, guys like Russell Wilson and RGIII will always have their durability and longevity questioned because they're smaller than the traditional NFL quarterback. Guys like Mike Vick have shown in the past that smaller quarterbacks often face injury problems just because of the beatings they have to absorb as part of playing their position. A 6'4, 240 pound man is not going to have his ability to absorb hits questioned. ANd as an added bonus his athleticism should allow him to escape a lot of hits as he begins to better understand blitzes and protection schemes.
Obviously this doesn't mean he will become Peyton Manning, but it gives him the best chance of any quarterback in a few years.