Their fourth line has been great. Center Ryan Carpenter and forwards William Carrier and Ryan Reaves have added energy as well as goal scoring. That line arguably has been Vegas' best this season, which is why the Golden Knights have struggled.
Minuses: Defenseman Nate Schmidt, who was suspended 20 games for violating the terms of the NHL/NHLPA Performance Enhancing Substances Program, will be out for the next two games. You can see how his absence has affected the Golden Knights; he's an elite defenseman who led them in ice time last season and was their second-highest scoring defenseman. Those are things you can't replace.
I think Vegas misses James Neal, who signed as a free agent with the Calgary Flames. This guy has scored at least 20 goals in each of his 10 seasons in the NHL (he has three in 18 games this season). Neal was the perfect fit for Vegas and has an edge to him. Vegas acquired center Paul Stastny, who is injured and has played in three games this season, and forward Max Pacioretty, who has two goals in 14 games. Those guys were expected to bolster the offense, and so far it hasn't happened.