Reese had a very solid initial draft, but beyond that, numerous poor drafts and free agent signings that left the Giants with a poor roster by the time his time as GM ended.
I think the two most important jobs of a GM are finding a coach and QB. Reese inherited a Coach-QB combination that would last together from 2004-2015. I don't have the stats in front of me as to how many QBs were drafted and coaches hired during those 11 years. But during that time, Reese was able to operate without needing to deal with those two biggest GM tasks. That's an incredible luxury, and I yet the roster got weaker, not better, after 2007.
I have to give him credit where it is due. A portion of the roster during those two Super Bowl runs were the product of what Reese was able to put together. But I also think Eli's won/loss record is a better reflection of Reese's performance. And during both Super Bowl wins, the Giants had to beat teams who quite frankly had better supporting casts.
So, I would agree, Reese was ultimately underwhelming as a GM.