The album works well in part because the songs alternate voices - musically, lyrically & vocally. 7 songs are written by Emily, 6 by Amy. The styles & rhythms vary. 'Rock and roll Heaven's Gate' instrumentally sounds very similar to Rick Springfield's 'Jessie's Girl' (a cool rock song if for no other reason than it rhymes the word 'moot'). This album does not deviate from the Indigo Girls terrific sound. The album gives the strong impression the Indigo Girls read unfavorable fan reviews about the 'over-produced' 'All That We Let In' (see for example the Amazon reviews), and responded by making 'Differences' a return to earlier sound schemes. So if you've heard lots of Indigo Girls songs and enjoy them, you'll probably enjoy this album. But vice versa is probably also true. 'Last Tears' musically reminds me of fresh, 70s sounds of country rock
The Indigo Girls keep their unassuredness on their sleeves, asking more questions of themselves than shouting answers to others. While pop singers like Christina Aguilera proclaim 'There Ain't No Other Man' and they've found their one true love, The Indigo Girls are consistently wrestling with all their loves, past & present, political & personal: 'Have I learned all that I'm supposed to learn?' from the song 'All The Way.'
The first 4 songs are upbeat and hopeful. But like older songs such as 'Hope Alone', 'Differences' includes sober songs like 'Last Tears' & 'Run' about the illusions of letting go of loves and the near hopelessness of living with unrequited loves. On a political level, 'They Won't Have Me' is a blues concession that so many environmental conservation causes will likely inevitably fail. But the Indigo Girls would not exist if they did not emphasize hope. And 'Pendulum Swinger' starts the album's rally with 'I see love and I like to make it happen' and 'You can't keep a spirit down that wants to get up again.' The Indigo Girls can't force change, and they don't believe silent frustration can create progress. So They Sing. 'It doesn't come by the bull whip. It's not persuaded with your hands on your hips. The epicenter of love is a pendulum swinger.' They express ideas with clear acoustic sounds, open air feel, & beats that make you want to clap & swing your hips on the 2 & 4 ('Little Perennials').
There are some songs you hear that are so good, that once you've heard them, you can't practically ask yourself: What would my life be without them? They are a part of your psyche. You can't imagine throwing them away. You can't "unhear" them. The Indigo Girls have created many of those songs for me. They don't just stand on a street corner shouting clever slogans and waving signs. They articulate complex arguments and ideas in concise ways, emotionally and intellectually. They live lives consistent with those ideals. They stay in the debates long after the majority has continuously opposed them.
A way to evaluate a relationship between 2 artists is to ask 2 questions: 1) How does their effect on each other improve the creation of quality art? 2) How does their effect on each other create a more positive social environment for everyone around them specifically, and the world in general? I don't know why we got so lucky that Amy & Emily met. The convergence of their artistries is probably larger and better than if they had never chosen to work together. I don't like to imagine a world where they had never met, or where they no longer choose to create together.