In the original trilogy, it looks like the Force is something mystical and almost magical but there are no overly impressive actions by any Jedi (compared with later works and legends)
Obi-Wan performs some mind tricks, senses the destruction of Alderaan and has a very unremarkable fight with Darth Vader before passing away. Also, the acts of Luke are also not that impressive.
Darth Vader Force-chokes some people but again, nothing remarkable happens in the first movie.
Episode V and VI extend a little bit, introducing some abilities (mostly telekinesis, mind tricks and precognition) but the whole possibilities of the Force are left mostly to the imagination (and that probably improves the movies).
Further works have then extended this through now non-canon materials. I remember the SW D6 role playing game introduced a lot of powers and details to the Force users.
Are there any interviews or comments by Lucas about how much or how little he had developed the full extent of the Force abilities? I.e., for example, are there interviews of him saying he had only thought of a general theme, or on the contrary stating he had it all laid out for further movies?