I'd have liked to have seen Glendening moved for a pick if it was possible but it had to make sense. As we've seen from Buffalo, Arizona, and Edmonton full on fire sales rebuilds have quite the low success rate. If we could have gotten a 2nd then I'm fine with it but as is there isn't much point to move him for less than an overpayment.
As for Nill I'm not sure how I feel. My initial reaction is positive as I'm a of the style of team he's created in Dallas and he hasn't been shy to swing for the fence either through the draft or via trades. He traded for Seguin, Spezza, Methot, Bishop, Janmark, and Johns; while signing Radulov, Hamhuis, Hanzel in FA. He's been able to get a #1C, #2C, #3D, and a #1G while giving up little in return, I think the biggest pieces he gave up were a young Reilly Smith, Loiu Eriksson, and a 2020 2nd round pick. Outside of signing two sub par goalies to long term deals he's also been very good at managing the Stars' cap space.
The one area I'd be somewhat concerned about is his drafting as he hasn't produced an enormous amount of NHL players since he took over. He was good in '13 getting Nichushkin, Dickinson, and Elie; and he also got them Honka in '14 but that's about it in terms of NHLers. They do have some intriguing prospects in the pipeline now and I think the '16 and '17 drafts should produce some talented players for them too.
I think as long as Nil has a good scouting team around him he is a top 5 or 10 GM in the league.