It's an intriguing new piece of the puzzle, to be sure. But the two-hour Lost Archive quest doesn't go quite far enough in pushing forward the overall series storyline, making it less essential for those who care more about Assassin's' open-world adventuring than the lore behind it.
The Lost Archive will blast an evening from your life, and give you something minor to chew on until Assassin's Creed 3. But this udder sac is pretty much drained.