I just finished the first draft of a play. It was a whirlwind experience; I wrote the thing in 12 days. When I first pitched it to a friend, he told me it sounded like a movie.
I don't often write plays, and generally for good reason. The last one I wrote crashed, burned, and exploded before Act One ended. Unfortunately, the rest of The League was caught in the blast.
But for me, writing plays are actually a lot of fun, provided I have an idea worth pursuing. Beyond that, they're also both relieving and revealing. They're relieving, because with screenplays, we're told to restrict our dialogue. To show, not tell. To write what needs to be said, and then figure out how to cut as much of that as possible. But with plays, it's all about the dialogue. The action is in the dialogue. The dialogue is in the dialogue (I wrote that on purpose). And the heart of the story is in the dialogue. It can all be found in the dialogue. Rather than writing and cutting down, I'm free to write, write, and when I think the scene might be over, see if I can write any more. (Granted, it's never good to overwrite a scene, but in plays, there's an opportunity to directly say more and for longer than in a film.) I like doing dialogue, and being able to cast off the talking restrictions of the screen is a great feeling.
Writing a play is revealing to me for the same reason. It reveals how much either can or cannot be said by dialogue and what, no matter the medium, is best said without words. I have always found plays more difficult, since I'm not allowed to show things as easily, blow things up as effectively, or transport my characters so readily. But, on the other hand, I get to use my imagination so much more effectively. Rather than just saying something is on fire, which it very well could be on screen, I am forced to conceive of how such a fire would be handled on stage, what lights, what sounds, and what effects would create the desired image. It's a great learning experience that transcends writing to directing, I believe, to write a visually stimulating, "special effects" filled story for the stage. That, to me, is truly revealing.