Nikitin looked really good on Columbus 3 years ago then his game just went downhill. I'm sure it has to do with injuries but if he's healthy and in shape then he's a decent defenceman. He's just not worth 4.5/season.
Indeed...he was a decent dman a few years ago and he just turned 29.
I cant remember where I heard it but there is word out there that his back issues have been a problem for a few years now.
That may explain the dramatic falloff in his play because he is not at the point in his career when this typically happens.
He was a solid NHL player before the back issues.
If he can manage to correct his cranky back he would be a solid bottom pairing (short term #4) dman and a decent option on the PP.
Thats a big IF though because it looks very much like his back issues are chronic and his career may be in jeopardy.