OK Lunja, my congratulations - you just proved that you can take criticism. This alone boosts your chances of becoming a successful artist. I've seen many student filmmakers of varying talent. However, the ones that couldn't take criticism never went anywhere.
You don't have to
agree with the substance of the criticism, but you must
listen to it as a favor to yourself. And let me tell you, if you are to work in this business, criticism is what you'll get day in and day out. 90% of the time, the criticism is valuable, even if not apparent at first. The best kind of criticism is the one where the critic is right, and has the right ideas about how to fix the problems. But even "poor" criticism is valuable.
You will eventually learn
how to listen. One example: when a studio exec (or simply a reader) tells you that the hero of your action script needs more "character background", as often as not, the truth is that your action is too slow or boring and has nothing to do with character background. You can put in all the character background you want, and the exec will come back with some other irrelevant notes. Are his notes still valuable? Yes, because even though his/her diagnosis and prescription is wrong, he/she is right in identifying the basic problem that
for some reason your script isn't working. That's valuable.
Finally, yes, on occasion you'll get someone who is just an ijit. Off the wall irrelevant nonsense. Guess what? Even then I don't come out "guns blazing". Why? Because you win more people with honey than vinegar. And that clueless exec might help me or hurt me in the long run... why alienate them?
See how it works in practice? I'm spending time writing a long post for you, with the sincere desire to help you in your quest. Had you come out "guns blazing", I'd chalk you up as another loser, and that would be the end. But instead, you were mature and smart. That's how you got me to give you some of my X-mas time
OK, onto your movie. Wrt. to acting, I intentionally didn't dwell on it, because it really can be very tough for a student filmmaker. In general, after the story, the actors are the hardest thing to get right in film. SpaceMagic makes some valiant suggestions, but that won't really work.
First thing is to fix your dialogue. Write it and speak it OUT LOUD. Not "read silently to yourself" but OUT LOUD. Further, I'll give you an invaluable tip:
record your dialogue onto a recorder and play it back. You'll be amazed at what you find. To make dialogue sound realistic takes years of practice, because realistic film dialogue is
not simply recording how people speak in real life. It is a special kind of film-speak. You do the unnatural and make it
sound natural. If you simply recorded how people spoke, it would sound extremely boring and full of useless ummms and hmmms. To get actors to do a good job of your dialogue, first and foremost your dialogue itself has to be good. What you have here is too much in the way of words - film is not a book you read out loud. Stop speechifying, fewer words are better. Economy. Less is more.
Next, especially when you work with amateur or near-amateur actors, try and get them to STOP ACTING. Really. When they ACT, they are wooden. Still, I have to say, I wanted to avoid the topic, because it would be criticising you for something you have little control over. Fact is, if your actors have no talent there's nothing you can do. I've tried giving them drugs, I've tried having them do strange things, I've tried almost everything. It doesn't work. Now, with a few exceptions (rare "natural talents"), even professional actors need to be coached by the director. What that often comes down to is not really talking about the role, but trying to get them to STOP ACTING. That's why many directors intentionally try to throw actors off balance - by means ethical and unethical (Polanski would drive his actors into rages by staging conflicts, Kubric would do 70 takes of a scene until the actor was like in a dreamstate, others would use sleep deprivation etc.). And with no-talent hacks and wannabees, no tactic works. Rarely does a student have access to professional talent. Hence, I didn't want to speak to acting in your short... there's nothing you can do about it (well, other than writing in such a way that it demands LESS of an actor to pull off a scene - if there is inherent visual/situational drama in your scene, you don't have to rely on the actor as much to manufacture the drama for you... this is another reason why action movies which rely less on acting are easier to pull off with wooden actors... which is why Steven Segal, Chuck Norris and other woodsters have careers - look at that huge explosion!).
Re-evaluate everything. Is boring camera angle "in a car" really something that will contribute to holding our attention? Really, we've only seen such scenes a trillion times. How about something slightly different. And no, I don't mean a pointless "point of view of a spider" angle. But there are many ways to show things, and you don't have to repeat the same old, same old we've seen and been bored to death by. Does staging have to be so unimaginative? Why don't you have your actors move in such a way that it holds our interest? Editing rhythms, do something that will keep us interested, instead of cutting at the most predictable moment. Use your imagination - that's all you have, since obviously you don't have a budget for a spectacle.
Be persistent in re-examining your project. Don't rest or settle for second best. You'll be better for it.
Good luck!