I suppose he got Kadri and Rielly on good contracts, traded for Andersen, and offloaded Phaneuf which are all good important moves. Andersen in particular was huge, and Rielly has obviously made that contract look like a huge bargain with the numbers he's putting up. But he also signed Zaitsev, Matt Martin, Polak (who was probably better than people want to admit), and Marleau to a $6mil+ contract, as well as moving second rounders for Plekanec and Boyle.
Dubas moved out the Zaitsev mistake, but it cost him Connor Brown. He moved out Marleau, but it cost him a 1st. He brought in Barrie (hey it looked good at the time) and Muzzin, but it cost Kadri, another first, and some decent prospects. I think those all addressed errors and oversights by the previous guy. He's also got some extremely good young players locked in, though I guess there's some concern he paid too much.
I dunno, I will reserve judgement until I see how he handles the upcoming mess of defense he needs to sign before next season. Typing the whole thing out makes it seem like they both have their ups and downs. Lou definitely got the rebuild off to a good start though, you're right.