Greg is a great team guy who will win you faceoffs and is a really solid PKer. His offensive skills have faded rapidly over the past few years as the Preds moved him to a more 3rd line role. He has good speed; it is no longer great. But he's injury prone and has no grit whatsoever. He's just as likely to kiss an opposing player as he is to hit him (read: not likely).
I think he's a serviceable 3rd/4th line center who should get the league minimum. He's really not shown the skill be a 3rd line center in the new NHL where the good teams seem to roll 3 scoring lines. But he's doesn't possess the higher energy, physical style that you normally like from your 4th liner.
I'd expect Ottawa to sign him for the league minimum, and he'll have a role similar to that of Rem Murray's in Edmonton this past season (when he was on the big squad). Though I would expect him to have more time on the PK than Rem did.
one other thing I'd like to mention is that oddly Johnson rarely misses a breakaway...not that he gets them much anymore...but still.
But any other time he has the puck in close, he's sure to miss. In fact, I was talking to Triggr a few years back and I'm pretty sure we called hard wristers into the goalies chest "Greg Johnsoning it."
He was solid on breakaways, but if he shot on a 2 on 1, all the goalie had to do was make sure he was centered and his logo would eat up the puck.
Johnson was a wonderful person and a good team guy, but there's a reason we didn't keep him on despite having a need for a 3rd line center and the fact that he had no bargaining power.