The Garden of Eden

Good atmosphere develops over first 16 measures. At measure 17 the listener is ready for something else but it doesn't come. I'd suggest coming in loud and major (chord-wise) at about measure 19 (keep 'em waiting just a little bit) and sticking it to the listener with a trombone to herald in the rest of the piece (just herald in, mind you, you don't want the trombones wiping out the rest of the ensemble as is their wont) and with the strings full-on as a backing chord then maybe a rising arpeggio from the winds. As to the melody, well it's your piece and you need to think on that but the overall religious feel suggests something hymnal - simple in terms of scope and rhythm but rousing and memorable. Then a closing section with the trombone more subdued and maybe finish with a violin soaring up to a held high note, final grand chord swelling and dieing, gentle gong/symbal clash at end.

A few comments, in random order:

1. You have published your score in concert pitch, which is unusual. Most conductors prefer having the transposing instruments (clarinets, horns, trumpets, etc.) appear in written (rather than sounding) pitch in the score.

2. Score layout: The instruments in your piece are not shown in score order, which makes things difficult for a conductor trying to find a particular part. Traditional score order is by choirs (groups of similar instruments), and is, from top to bottom:

1. Woodwinds (flutes, oboes, clarinets, bassoons)
2. Brasses (horns, trumpets, trombones, tuba)
3. Timpani
4. Percussion
5. Other Instruments (harp, piano, celeste, organ, voice, etc.)
6. Strings (violin, viola, cello, contrabass)

Within each choir, instruments should appear in pitch order, highest to lowest, with certain exceptions (such as the horns, which appear above the trumpets). You have got most of that correct, but the string choir needs to be moved down to the bottom of the score, and the timpani should appear below the brasses and above the marimba, glockenspiel, and harp.

You should also bracket each choir, and connect groups of the same instrument using braces.

3. You have too many parts on certain single staves, and you are not using voices consistently on those staves wherein you have written multiple parts. Ex: on the violins staff, you have two or three poorly-defined violin parts which sometimes cross or are written as chords in voice I. It is not possible to tell who should play what, or if you are writing double or triple stops in many places.

Best practise is to use a separate staff for each part (i.e.: Violino I, Violino II) and if you wish to write divisi sections in either or both of them, then use a second voice to do so, not chords.

Where you do need to combine two parts on a single staff, the long and short instrument names belonging to it should be modified to indicate that. In other words, you should not write two clarinet parts on the same staff unless the staff is named 'Clarinet I & II'. Again, use the words unisono and divisi to indiate where both clarinets are playing together or separately, and use separate voices and not chords.

4. Harps are scored on two staves; using a single staff denominated in bass clef (as you have done) tells the harpist you expect him to play everything with the left hand. Unless you are scoring for a troubadour harp, as opposed to an orchestral double-action harp, you need to take account of pedal changes, too, and indicate the string tunings (in pedal order, from left to right) and where in the music the pedals must be changed. This is particularly important in music such as this which is highly chromatic with many accidentals. Every accidental requires a pedal change, and you must be careful not to write parts which require changing two pedals on the same side of the harp at the same time. Also, remember that the right hand cannot reach as far down the harp as the left, hand, so don't write low arpeggios which require both hands to execute.

5. You have not specified (a) how many timpani are required, nor (b) to which notes they should be tuned. Avoid requiring a timpanist to re-tune in mid-piece unless you give him at least two measures of rest in which to do it. Timpani should not ordinarily be required to play chromatically.

6. Horn parts can be written in either bass or treble clef; unless there is a reason to write it in bass clef, however, it is better to stick to treble. If you publish your score in transposed notation (as you should, as noted above), that shift to the bass clef in m.5 causes most of the horn part to be written on ledger lines above the staff. Even if you publish a concert pitch score, however, the parts for the horn players must be printed in transposed notation, so while the conductor would see a bass-clef horn part written on the staff in concert pitch, the horn part itself would be written above the staff.

Very helpful @recorder485.
I've gleaned some of this from Orchestral templates but it's good to read the explanation of why this is so from someone in the music business.
Many thanks.