I also tested the mission and here's my list of comments:
The more important issues:
Firstly and most importantly, the Deimos did not jump out to me. I had to open the mission in FRED and find out what's causing the problem. Theoretically, it should have jumped out in the way you had done it, but it didn't. The thing I did was to increase the Deimos's engines' integrity to 50% for each engine. In retail FreeSpace, this shouldn't be a problem. It's probably an FSO-related gameplay change. Still, since the decisive majority of the community uses FreeSpace Open, you should optimize your missions for that. Retail missions in FreeSpace Open sometimes do at first inexplicable things.
Secondly, the player receives the "Depart" directive before the Deimos actually jumps out. That way, you jump out "legally" and still fail your primary goal. My suggestion is to trigger the Depart directive with the has-departed-delay SEXP.
Thirdly, only a few wings had Initial Orders set. Without an Initial Order, ships will perform a very ineffective "Attack anything that comes within your sight." Still, it would be better to set an "Attack any ship" order with a high priority for fighter wings, and, for Alpha, a Protect ship -- GTCv Julius order to make the player's wing form up on the Julius. The Protect ship -- GTCv Julius should have a lower priority.
And least importantly, the transition between Briefing Stage 2 and 3 is odd. It looks like an invisible hand drags the Deimos icon out of sight so that Alpha's icon can replace it. My suggestion is to delete the Deimos icon in Stage 3 and create a new one for Alpha. Deleting an icon in Stage 3 will not make the icon in former stages disappear.
The less important issues:
- The mission needs a spellcheck. Most importantly, get your apostrophes right, capitalize "Shivan," and use commas before (or after, if your sentences is so) the addressee. "Jump out pilots" --> "Jump out, pilots."
- For every message in a send-message-list list, you give the delay of "300." This is in milliseconds, so with a build without simulated speech, the messages would appear practically all at once, making them hard to follow.
- Use the Y-axis. Currently, all the ships appear on the same altitude level. Place some wings or fighters a little bit up or down, because it looks more realistic, and it's easier to track on your rader how many enemies you still have.
- If you feel like, you can add a "Destroy all fighters" directive. If you do it like is-destroyed-delay -- (list of hostile wings), then you will get a counter that makes tracking the numbers of hostiles easy.
And on the positive side of things:
The mission is stable enough apart from the Julius not jumping out part. The mission is generally easy, unless you are stupid enough to shoot down a bomb while it's near you. I personally prefer easier missions over more difficult ones, so this mission's difficulty level is a positive thing. Be careful, though, because changing minor things like giving orders to enemy fighters to intercept might turn the tide around.
It is also good that you did not have any more fighters randomly jumping in at various points of the subspace tunnel. It's more realistic this way.
Dialogs are ok, apart from some spelling and punctuation mistakes. It's good that the final dialog starts up only after all the hostiles are down. Therefore, the player doesn't need to divert his attention between combat and reading what's going on.
It is commendable that some subsystems are damaged also, not only the ship's hull was reduced. I like it when a FREDder, especially a novice one, pays attention to details.
@Kara: Is there something else that needs tested? I see that the threads here are rather old.