Total Recommendations: 2
Both series feature a post apocalyptic setting where the remainder of society has been diverted to domed cities. The protagonists each set out on unique journeys outside the domes that lead them to uncover key points about the plot and world they live in. Although the domed cities boast strict government and rife technology it's widely desolate outside of them. Ergo Proxy carries a heavier tone than Freedom, and is the more developed story of the two. Freedom is short and easier to follow, but has noticeably less depth. If you've seen one you will probably enjoy the other. Regardless, they present similarities.
Both are fantasy series with girl protagonists that transform and have powers. Both contain fairies to some extent. They share the same general theme, but have differences as well. If you enjoyed Leviathan you will probably enjoy Neptune.