Very nice work on Over the Rainbow. You clearly have a command of 6-part vocal jazz, and I think the arpeggiated patterns and rich harmonies you chose serve the original very well. I would not be surprised at all were I to have come across this arrangement in a sheet music store.
Your original, Secret Diary, is a solid original tune. However, what strikes me most of all about it is that the arrangement of it is several notches lower than your work on Over the Rainbow.
This is not at all unusual. In fact, Id say its extremely common; when an experienced arranger works on one of his own tunes, the results are often very, well, plain.
The reasons for this are simple: the arranger is not thinking as an arranger. Shes thinking as a songwriter. As such, the focus is to get the song down in its most basic form: melody, lyric, chords. The result of this is (often) more whole notes, triads and repeated patterns, and fewer contrapuntal lines, polyrhythms and countermelodies.
And yet, an experienced arranger who works this way is only working at about 20% of her creative capacity. The difference between an average and a great a cappella arranger is that the latter is able to emphasize the strengths in a songs lyric, rhythm, harmony and melody to strengthen the mood when translating into voices. To avoid this step is to lose the value of having a song arranged; it's a demo, not a final recording. A mock-up instead of the real McCoy.
My suggestion is this: take a little break from the song, step back, and then approach the arrangement you have been given as an arranger. What can you do to bring the song up to a higher level?
Example: What is the focus of the introduction? What mood is being created? How can you use the various elements of sound (pitch, duration, timbre and loudness - which in combination become melody, harmony, rhythm, syllable choices and dynamics) to emphasize the mood? Remember, just as when youre arranging another persons song, you dont have to remain stuck to the original chords. Perhaps an open fifth would serve you better in the opening, rather than the triad you have there now? More ominous?
And the first lyric is listen to the voices in my head, which screams out for some creative a cappella treatment! Perhaps the open fifth strikes, followed by some spoken murmuring, growing into fragments of lyrics later in the song that are echoed by a second singer. The introduction can be extended and turned into something very cool, unusual, and impressive. People wont know your song, but Ill bet theyll be leaning in to hear it after a moody, compelling introduction.
And thats just page one.
If you run into snags or find yourself in creative block stasis, perhaps listen to some music that inspired your song, or bounce the work youve done so far off a fellow arranger. A little outside perspective in the form of other music or another opinion can help you get back on track.
I hope this advice helps, and look forward to seeing where you go with the song!
(Pending his approval, well include his original song - both the original arrangement and what he does with it after reading my response - on casa.org in the future.)