To be perfectly frank, the animation was what the show's been leaning on, too. While I greatly enjoy RWBY, the plot is average at best. Volume 3 has been a substantial boost in writing, and the show's had a boost in the technical aspect of the animation (especially regarding facial animation and such), but it's accompanied by a frankly massive drop in the quality of the fights. None of the other animators had Monty's grasp of flow in combat, let alone the ability to animate the fights and make them feel real. The choreography, and the incessant jump cuts, have been severely detrimental to all but a few of the fights in this volume.
The fights are technically faster, but that's to try and make up for the fact that the flow of motion is slower. Not to mention the fact that none of the blows (again, certain fights exempted) actually have any weight behind them. Monty's great fondness for Hong Kong action films shining through there, to be quite honest.
This isn't the death knell for RWBY, but it's adding a big old weight when RWBY just finished getting past the loss of Monty.