Neal is the key to this deal. The Pens have him under control for this year and next with a cap hit of $2.875 M. He will play on the top two lines and can score. He had 21 goals in 59 games this year for Dallas, following up campaigns with 24 and 27 goals, respectively.
Niskanen is a bit of an enigma. He was taken as the Stars first pick in 2005 (right before James Neal) but has seen his playing time (and his +/-) decrease each year. This season he has been playing less than 16 minutes per game but is only a -1 on the year (-11 and -15 for the two years prior). If he can regain some of what he showed in his rookie year, he'll be a steal.
I'll be sad to see Goligoski leave. I think he didn't get the credit he deserved in Pittsburgh. Letang went through growing pains before he became the defenseman he is today - I think Goose was on the same path. Hopefully he succeeds with Dallas.
The really interesting part is that the Pens have set themselves up for trouble following this season. Goose for Niskanen is nearly an even move against the cap (Goose counted nearly $400,000 more against than Niskanen will). Neal will count $2.875 M next year. That means the Pens are either setting themselves up for a blockbuster trade, salary-wise, or they will be limited in how they can spend this summer (limited as in about $3 M left to sign 5-6 players).
For the remainder of this season, however, I like what I see. Niskanen isn't that much of a drop off from the role that Goligoski was playing (except maybe on the power play) and Neal is a definite upgrade at forward.