While I enjoy crafting stories in my mind, I have always struggled with the screenplay as a format.
I think its constant, unchanging characteristics force the writer to imagine elements that subtract rather than add to the story. For instance:
--The fixed length. Makes the writer come up with "filler" scenes.
--Dialogue. Makes the writer script many more dialogue scenes -and speech in general- than necessary.
--The lack of language that accurately portrays what will be seen on the screen. Not allowed too many paragraphs of description, the writer falls back on dialogue.
--The three act structure. A good structure, but sometimes robs the story of interesting, unexpected story beats that would be more interesting than traditional act bridging plot points.
I am not saying the screenplay is a bad format or that I don't like it. I just don't think it lends itself to the way I write stories. I am interested in hearing whether you find the screenplay suitable to your storytelling style or not and why.
As odd as it sounds, I find the screenplay format extraordinaly liberating. The economy it requires allows me, as a writer, to focus. Even the very best prose writers get sidetracked at various times in their novels.
If you think a script should be constant and unchanging, I'm afraid you're mistaken. You should always choose your words carefully so you don't repeat when possible. Change sentence length, rhythm, etc. Yes, you can still do all of that while writing a screenplay and still stick to what's expected.
As for a fixed length?...there really isn't a fixed length. Rather, its more like a fixed interval. Anyone who says you have to have such and such on an page 55 and the screenplay has to be almost exactly 110 pages or whatever, I don't think that's the case. For sure, you can't have one 90 pages or one that's 200 pages or anything completely out of the norm, but 100-130 isn't really an issue. That's a half hour's worth of wiggle-room, more than enough time to end the story the right way.
There should never ever be "filler" scenes. If you find you have these in your script, you don't have a good enough story, or you haven't gotten your mind into the story enough to really know it.
As for dialogue, if you can tell something in the story without a single word being said, do it. There are a lot of quotable quotables in movie history, but there are an awful lot of spectacular film sequences that don't have a single word of dialogue. When it comes to describing a scene, this touches on the biggest difference between the screenwriter and the prose writer. If you write in prose, you are the final version of the presentation. It is your job and your job only to convey to the reader exactly what is going on. But in screenwriting, that's not the case. When you go to a movie, you don't read a script. You watch it all on the screen. It's not only your job to convey to the audience what happens, it's also the director's job, the actors' jobs, the cinematographer's, the crew, everyone. That's why you limit your description to only what is necessary for everyone else to do their job later on.
But description shouldn't just be bland. If you read professional screenplays online that have been produced, you might notice they seem kind of lifeless at first. At least, that's how some of them have seemed to me. Some of my favorite movies (not all), I'll go and read the script and be struck but how boring the script seems. Not the story, just the way in which it was written. The only conclusion I can draw from this is that some who are already professionals, already have a reputation, all of that, are able to write the story in the simplest possible way and that is enough for them. They get the story across, and then they can explain it more to the director, agents, producers, etc. in meetings. Well, if you're writing a spec, you don't have that luxury. So make it interesting. The story ALWAYS has to be interesting. But you, as a spec writer, need to WRITE it interestingly, if that makes sense. And you can still do that concisely to meet expectations. It's very a subtle talent.
Finally, structure is a universal thing. All stories ever told, no matter how crazy they are, no matter what order the events were told in (or out of order)...all have three acts. Beginning. Middle. End. It's fundamental, like the sky is blue. Even if you want to write edgy non-conformist scripts, you have to at least master basic structure first. You can't do calculus if you don't know algebra. That sort of thing. Even some of the great existensialists and others in the mid 20th century who told the most elaborate stories that didn't conform to normal structure...well they all spent 20 or 30 years telling "regular" stories before they tried something more exotic.