I just completed another draft of a feature script. I really like doing multiple drafts with reading space in between, because each new version is usually an improvement on the last. I find the process similar to the way I paint (in multiple thin washes). It takes a while to build up the color and each wash builds depth. Similarly, I find each pass on a screenplay or piece of fiction also builds more depth. The theme emerges, the weak points become clearer, and the diamonds hidden amongst the pieces of coal finally shine.
I can't stress the importance of rewriting enough. Yet this is often the thing new writers fear the most. Fear, schmeer. Brave writers are happy to start over from scratch (page one rewrite). Don't worry, you'll remember the good stuff and often surprise yourself with new material. I find if there is a lot of work to do on a draft, rewriting from page one is easier then cutting and pasting and adding in new scenes. At the risk of metaphor overload, It's like knitting a sweater; if there is one small hole, go ahead and repair it. If there are many holes, you often end up with a big messy pile of yarn. In this case, go back to your pattern (beat sheet) and start again.