To begin with, it's cast in four movements rather than the three Vivaldi would eventually settle on. Some concertos in L'estro armonico have as many as five movements, which suggests that Vivaldi had in mind the trio sonata and concerto grosso layouts favored by Corelli and other composers of the day and earlier. The "extra" movement here comes first: an Andante, beginning with highly dramatic announcements from the full ensemble in the dotted-rhythm French manner. This gives way to a rather tense response from the soloists. Tutti and solo passages alternate, with the second solo section more florid than the first.
The Allegro assai maintains the mood of the first movement, but now at a much faster clip, with the soloists (often singly or in pairs) presenting hectic material that sometimes is little more than flying scalar sequences. The style is very much that favored by Corelli, although the practice of giving the soloists their own individual material is more often found in the concertos of Albinoni.
The brief, transitional Adagio, too, owes something to Corelli, although it also hints at the more mysterious passages to come in the slow sections of Vivaldi's Four Seasons, particularly the "Winter" concerto. Vivaldi finally breaks out of the Corelli mold in the concluding Allegro, although he continues to employ the Albinoni technique of presenting the soloists as individuals in subgroups. The abundance of thematic invention and the exploitation of string colors are elements that would dominate Vivaldi's later work, and set him apart from many of his contemporaries.