It's good to see that there are still some enthusiastic people trying to make cinematics, so I'd like to credit you about that before my review.
Your part4 is definitely allot better than your previous parts, you see a growing process in your cinematic parts, so good job.
Overalll I am giving you a 3/5, it would have gotten my 4/5 if some parts (which are described below) were better.
All of this is just feedback on your cinematic, so pointers on things in your cinematic that can be thought about when your making another cinematic.
Terrain and Atmosphere:
Your terrain can use allot more tunning, it has improved since you first started your series, but try using the deformation tool a bit more, in non walkable area's like forests. try building some mountains here and there.
Try to avoid using deformations that critically heighten up your terrain tho, specially on paths, cause where people walk, terrain is mostly gradually heightened or lowered.
Additionally, there is room for more detailing, don't forget your can throw in allot more detailed terrain cause this is a cinematic and terrain creates a potion of the viewers pleasure.
Also see where you can toy around with fogs etc.
Be careful with fade filters, don't use 2 fade in filters over one another like you did, always make sure you fade out of your first fade filter before fading into another fade filter.
Story and Dialog:
Your story over all 4 chapters is to marked decently, there is still room for more specific character based scenarios, be carefully with releasing too much parts and suddenly stopping a cinematic, like you did in previous parts, it can cause quite the confusion with people.
Your dialog is ok, nothing too fancy, try to play around with words, and don't nessarilly create cliche sentences.
Camera motion and Control:
There was nothing really in this part that disturbed me in particular, be careful tho with hard switching from one to another camera, that have different angles etc, then your motion can become quite blocky, so to speak.
Your camera placements were decent, even tho you allot of the same AoA, angles of attack, try toying around a bit with that, the AoA not only defines how the viewer is looking at the event or unit, but also the terrain at the background.
Animations and Interaction:
I specifically like the starting slow animations where illidan blew things up, well executed.
Other than that, there were no real issues regarding animations as far as I could see, try using those tho, when units are interacting with another, it gives another dimension of reality to your cinematic, that units perform certain motions when they talk.
The interactions with units among each other was sometimes rather basic, "I want this, you don't get it, I kill you, etc"
Try upping the interaction moments units have with one another when they do.
Music and Sound:
Use the music you imported as sounds and not as music, this way they can be played louder in the game, additionally, sounds can be edited when you double click them, that way you can decide on what level you'd want to play them in the game,
Additionally, when you switch from one music track to another, use sounds and let one track fade into the next one, this gives the viewer the notion that something else is about to happen, but it's less obvious.
The sound when Arthas died, was compared to the music on the background way to loud, keep in mind you make sure that the sounds for animations or effects are not either to loud or soft, but they contribute to your music.