The Oline was the biggest problem this year. The giants had started to re-tool by drafting Justin Pugh and Round 1 this past year. They had counted on Baas and Snee to anchor the middle for at least another year or two. That was a mistake, b/c both were lost to IR this year and can't be counted on in the future (Baas has just been injury prone and rumors are that Snee's injury is career threatening). The center of the giants o-line was horrible this year. Pugh was actually pretty good at RT, but Beatty was bad at LT this year (and broke his leg in the last game). So the giants probably need to address at least 2 O-line positions in FA/draft. I think one high draft pick and a late rounder, plus a good FA signing will do wonders for the line.
As for D-line, I don't think the giants are in as bad shape. They spent a 2nd (DT) and a 3rd (DE) on d-line in the last draft which should help with the youth. Both players had decent playing time and showed potential. There are some questions though. They have some major FA decisions. Linval Joseph (DT) is a FA. Giants will make an offer, but like Barry Cofield, he may get a larger one elsewhere. Giants may need to overpay here to anchor the center of the line. Also Tuck is a major FA decision. He is old, but did produce well towards the end of they year. He has stated that he wants to remain a Giant. The Giants will probably offer him something, but he will probably get a higher offer elsewhere. So it comes down to how much is the difference and how much "money talks". They other question is whether JPP will ever return to 2011 form. He has been injured for two years in a row, so there are serious questions about him. The giants may bring in a cheaper FA vet to compete for the DE spot.