First half of the season was pretty Jordan Jeffersonian, but he turned a corner over the last 4-5 games, starting probably with the Alabama performance. Overall I'd give his season a C+/B-, but he was trending in the right direction.
It's hard to pinpoint how much of the initial struggles were due to his own limitations and inexperience, or that of his teammates. A lot of the issues had to do with the surrounding personnel. While it's true he was holding the ball way too long at the beginning of the year, he was being protected by a makeshift OL that was down three starters, including an All-SEC left tackle, and was forced to use two true frosh on the right side. As the season went on and the OL started to gel, he grew progressively more comfortable and decisive in the pocket.
In addition to the OL problems, there was not a true "go to" WR to be found this season (miss you Rueben

). Landry and Beckham emerged towards the end of the year, but both are of smaller stature and more suited to be slot guys. The offense was really missing that big framed WR to target in the RZ, which partially helps explain Mett's rather pathetic TD total (11). Hopefully the big JUCO WR they just signed fills that void.
I think he has a chance to put it all together next season, especially with the continued development of the rest of the offense, but his occasional bouts of carelessness are worrisome. JaMarcus Russell or Matt Stafford is probably his ceiling on the college level - big numbers over the course of a season, but individual moments of derp.