The argument could be made that the Buffalo Bills made one of the biggest Free Agency signing this offseason. Obviously the Denver signing of QB Peyton Manning dominated the early headlines. Big time. And it should have. That was obviously a huge signing, which may have changed the shape of the AFC West for the next few years. It also has a ton of risks, too, given how obsessed you are with previous injuries.
The Bills, however, spent $100 Million to sign DE Mario Williams (obvious funky contract rules in the NFL apply). This signing was in conjunction with a $27.5 Million signing of DE Mark Anderson. Going into the offseason, it was pretty obvious that pass rush was a huge area of need for the Bills. It looks like they have decided to wrap this up pretty nicely.
That said, there are still a few holes on that defense at both LB and in the secondary. Obviously, adding some linebacker depth would help with the pass rush and the run defense - but, the Bills might decide that the added d-line strength is enough to compensate for any potential problems on with the LBs.
I would expect them, therefore, to look toward fixing problems in the secondary in the coming draft (maybe S Mark Barron from Alabama or CB Stephon Gilmore if everything lines up perfectly).
Offensively, you've got to imagine that the Bills would be pretty happy to snag WR Michael Floyd if he is available. Even though the Bills have WR Stevie Johnson, they might want to bolster Ryan Fitzpatrick's weapons going forward.
The loss of OT Demetrius (Demetress) Bell and the fact that they have Casper the Friendly Ghost playing LT leads one to believe that they might also add some depth on the o-line.