Music that is built on Markov Chains i.e. music that adjusts the probability of the next note based on the previous note or notes, that way the ambience can be more coherent, and the N-grams can be categorized by functional harmony or lack thereof, which can allow for thematic changes.
Music that has more than 2 instruments, or music that uses more complex chords.
Music that has natural sound effects on the side to induce realism, or maybe percussive instruments to add texture.