Honestly, one offense, the running backs and QB's do stand out to me. Playing against Stanford their QB completely destroyed my better than average secondary (and I usually have pretty decent pass defense). Playing against Michigan State, their 91 rated RB showed some flashes I hadn't seen from many others, though I think offensive line play is as big a factor in how well a RB does.
On defense, the only difference makers I see are DT's and linebackers. An all-star defensive tackle can make it difficult to run the ball up the middle unless you have a superstar set of guards and center. Also, superstar middle linebackers make running the ball difficult in general. Up the middle and they'll make a tackle. Run outside, and they race to that side to make the tackle.
All of that being said, I think the superstar WR's and superstar safeties really are under appreciated in the game. A great WR will usually catch balls when he's open, but it doesn't seem like they get open more easily than anyone else or make the spectacular deep catches more than anyone else. I play with a team that has a FS as one of their impact players and I just don't get much "impact" from him. Sure, he makes some plays in run defense because he's a "big hitter" but he gives up a lot of passes thrown in his direction.