Green_Hilltop: Wasn't it also a bit more accessible, eg. that even when you start out late as Jedi, you can still train and become a great one like Luke did. And there was no that Jedi code. The second trilogy put more flesh and depth to it but added restrictions - you can only be a Jedi if you start out young, otherwise you won't be able to enforce the code properly and so on. And it's determined from your birth if you'll be able to be a Jedi or not. And of course, it adds the wonkery of having a "more midichlorians" contest and thus being better with the Force just because of genetics and not skill or wisdom, however Anakin could be explained as an exception, being born out of the Force itself, if with other Jedi the midichlorian count doesn't influence their mastery of the Force.
We never see any young Jedi since they are all dead in the latter trilogy but in the prequel Yoda is quite clear that one should start when one is young and why he's against Quigon to take on Anakin as a padawan because apparently he's too old (like 9..) and he's too close to his mother, you are supposed to be free of emotions like a monk but at the same time have compassion for human life.
As for skill or wisdom vs genetics, I don't think it's much of a difference between the movies in essence (even if it's easier to presume that the old trilogy holds this better) as for what Yoda explains about how one must give oneself to the force and give up on Eartlhy bounds as opposed to Anakin in the prequel, full of emotions and wants the force to be all-powerful and erase his personal problems.
It's definitely partly genetics though but I think they add in the extended universe that there have been non-force wielders that apparently learned it through experiments, training or utilize some ancient Sith/Jedi artifact that stores the Force but I don't think much of these is the focus on in either of the trilogies.