He WAS underrated, but this last season has opened some eyes. I think he's just about where he should be in most peoples eyes. Deceptively good offensively, but not great; will never be a goal scorer. Amazing defensively, though lacks the strength to push anyone off the puck but makes up for it with excellent positioning and stickwork. Overall the ideal 3C who with the right linemates (like now) can be a serviceable 2C on a good team, but on a cup contending team he must be on the 3rd line.
Another thing that makes Nielsen valuable is that he is one of the best all time in shootouts/breakaways. ***** and moan about the rules all you want but the fact is that those are valuable points. Nielsen also recently added another move to his patented backhand roof rob (the 5 hole snapper), so maybe his percentage will even go up.