Even though Biograph would limit him to one-reelers, DW Griffith had ambitions to move on to longer films. Once or twice before this he had followed a short up with a sequel to be released a week later, but this is his first genuine two-parter, making a full, coherent story. Although Biograph insisted it be released as two shorts, many theatre owners cottoned on and showed it as one film.
Wisely, Griffith chose to expand upon a story he had made a loose adaptation of before, Enoch Arden having been the inspiration for 1910's The Unchanging Sea. Covering a lengthy timescale, the material is also perfectly suited to a longer running time.
Griffith clearly realised that if cinema was going to flourish as a serious and unique storytelling medium, it would not only have to develop in how it conveyed information visually, but also become more subtle and naturalistic. Around the time of Enoch Arden he was really striving to perfect this, and the two parts are like a showcase for everything he had developed so far.
Griffith opens by introducing each of the three main characters with a single title revealing their name only, followed by a shot for each which serves as a brief yet meaningful introduction. Then, without resorting to another title card, he sets up the love triangle with just some careful positioning of the three actors we have just met. This economy of expression would later be taken up and developed by Cecil B. DeMille and John Ford. The use of props by actors to reveal character or emotion is also beginning to develop. In the scene where Annie Lee watches Enoch's boat disappear over the horizon, she stops to wipe the lens of the spyglass perhaps to see the boat clearer, perhaps also to wipe away a tear.
Griffith was also beginning to develop the emotional impact of his camera work. He had around this time been experimenting by throwing in the occasional functional close-up to clarify an object or action. Here however, in the scene where Annie gives Enoch the baby's curl, he briefly moves the camera closer to the actors. The close-up is not to explain the action, it is to draw the audience into it and makes us involved in this poignant moment. This is a really important breakthrough.
Please see also my comment for Enoch Arden Part II.