A good story will leave minor things open ended on both sides questions about what happened before (allusions to the clone wars in ANH, mandalorian wars in KOTOR), and what happens next (ending to KOTOR and ESB). This gives a sense you are experiencing a snapshot of a living universe rather than a structured story.
"There is another" was done almost in passing, most people who saw the movie probably didn't catch it the first time. "Why didn't you tell me?" was more philisophical, not something at the end of the movie that I was burning to know. Luke calling out to Leia was something that more piqued my interest.
These things left the movie open-ended but they were interesting side notes that not tied directly into the main plot.
The story telling of KOTOR2 placed alot of emphasis on open ended plot threads, begging for them to be answered. If ESB was presented like KOTOR 2 those open threads would have been as follows:
"There is another" - changed to "No Leia will save the galaxy"
"Luke I am your father" - some long speech about the duality of the universe ending with Vader saying - Obiwan didn't tell you, you exist because I chose the darkside. Luke falls, cut to scene of falcon flying away, roll credits