DW's best move was getting Thornton. He made his GM career off of it. Everything else went downhill from there.
It's a bit reductive. As was (painfully) discussed elsewhere, he had a league-best first ~5-10 years of drafting, finding a lot of NHL regulars (and two all stars in Vlasic and Pavs) in late drafting rounds. While those years were so good that his entire tenure can in some analyses grade out as "best overall" the truth is that his drafting fell off very hard in the 2010's, where he was mediocre at best and bottom quartile often.
On trades, he made the Thornton trade, and he also made the Boyle trade and the Burns trade, all three of which were massive for the franchise. He then tried to run back the "franchise defining trade" game with Karlsson and Kane, neither of which worked out anywhere near as well as the Boyle/Burns/Thornton trades, and in my personal opinion (which others def disagree with) were both huge misses although both looked pretty exciting at the time.
Lastly, as has been discussed elsewhere (
@The Nemesis had a great post on the main boards), he for whatever reason decided to lock in our 30-ish core players (incl the EK's) to 6, 7, and 8 year contracts with NTC/NMC's from 2017-2020, and thus gave us the massive hangover we are still recovering from. The final "vodka shot at 3am" of this hangover was the re-signing of Hertl which I put fully on DW's shoulders.
He gave us 20 years of playoff contention, a bunch of years where we thought we were contenders (only proved out we weren't because of depth or injuries or star players choking, pick your poisonous opinion), and he left us with one of the worst cap, pipeline, and competitiveness situations the league has ever seen.
So it's a huge mixed bag but I would hardly say it was all negative but for the Thornton trade.