The Cabinet of Dr. Caligari is arguably a more experiment film for the period. It experiments with the bounds of the stage and the role of film in relation to translating stories through that medium by changing the usual geometry of a set in a way that exaggerates the space. There is a particular shot of a house sticking out across the frame with the monster walking off into the night (as seen below) and the unusual angles of the set and space heighten the fantastic and surreal nature of the story itself. The film becomes an experience of abstract spaces and planes of existence.
The film is extremely haunting. Roger Ebert dubs it the first "true" horror film, which would fit very much in line with an established lineage at this point of putting the true nature of reality onscreen. This film heightens that reality but doesn't shy away from the brutality of what humans can do to other humans. And that is a defining feature of early silent films from what I've seen. There isn't much of an aversion to portraying the woes of life as they are. The rounding of edges in regards to depicting murder, rape, death, poverty, hunger etc... seems to develop as society becomes more complex, technologically advanced, and politically nuanced.
So The Cabinet of Dr. Caligari takes that blunt directness and translates it into a horror film. And the film is interesting in that it establishes a paradox for the "monster" of the horror film. The Somnambulist is a “villain” in the sense of Frankenstein. He fights and is violent but only by the bidding and prodding of his master and environment. Everyone else sees him as a threat so he responds in kind. With the mad doctor running his side show we see a glimpse at the origins of the true “villain” “horror” film genre, where the monster is not necessarily evil or bad but being directed by a human who has corrupted him. This moral ambiguity which is revisited later in Frankenstein is reflective of the attempt to translate realistic portrayals of people onto the screen and their true natures and this inherent duality is part of that.
And the style serves to heighten this dual nature of good and evil by creating a world that strikes lines and shadows in ways that show a duality. Apart from that this film is really a mother to style in filmmaking. It introduces the ways in which a filmmaker can use angles and geometry as well as design in establishing a unique visual language that relates to the themes of the story and other messages the filmmaker wishes to suggest. Hitchcock notably followed this precedent.
In addition to the style, the film also gives birth to the notion of the "twist" ending with the last scene suddenly throwing everything we just saw up in the air as to whether or not it was a hallucination or actually real. Horror films since then have borrowed this device and used it as a template for their own structures.
On a performance level I think it's interesting to note how at this point actors were making big, grandiose gestures so as to make it absolutely clear to the audience, who were still somewhat new to this medium, what is going on on an emotional level and story level. The performance style of big over-the-top gestures also demonstrates film's place in society early on as a sideshow or a Great Big Circus, and so the storylines and gestures of the actors were "Big" as well to go hand in hand with the notion that it was a trick show and not high art or literature compare to theater.