I wouldn't go as far as an "F" in free agency, but I'd probably go with a "D".
For example, he way over-invested in LB when he could have spent that money on the D-Line. There were several guys who would have made a big impact there this year. Then he wouldn't have had to use an early 2nd round pick to acquire (and then pay) Sweat. That's just a failure when it comes to allocating resources.
For as much as we spent in FA, I can't think of a single impact-level guy he brought in. Yes, he had to spread that money out quite a bit because there were so many holes on the roster, but he has signed a whole bunch of meh.
Another example...the o-line was a massive concern coming into the year. Nate Davis was the big addition there. Yes, part of the reason he hasn't had an impact is that he's been hurt. But when you sign guys that have a history of being hurt and they get hurt, that's kind of on you for signing them. And even when he has played, he hasn't been all that great.
Can you give any counter examples that stand out in his FA signings that would call for a better grade?