[link to original on tumblr]
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I figured out some of the electric piano part, but I'm still not very sure of it. It doesn't help that Argent's Hohner Pianette has a brighter sound than the generic "electric piano" voice on my keyboard. I plan on getting a Nord keyboard eventually, so I can use the Hohner Pianette samples from their library (along with the Vox Continental, the mellotron, and probably some others), but that's more than four times the total amount of money I currently have, so it's not an option.
In any case, there seems to be some similarity between this and "She's Coming Home" in that the verses are pretty much just E major and A major. There's also a similar descending line; where "She's Coming Home" goes diatonically from E to B, "Is This the Dream" has E to F# - almost a complete E major scale.