I'd argue that none of the original trilogy was completely self-contained. They all worked as films, but even in the original Star Wars (before it picked up the subtitle) we see things are are given snippets of information that only come into play in later films, or even the prequels. We don't know how the Empire supplanted the Old Republic. We don't know what went down between Vader, Obi Wan and Anakin. We don't know about the Clone Wars, or the Sith or Luke having a sister ("no, there is another!" - Empire Strikes Back). The list of unexplained references and circumstances goes on and on. That's actually one of the things that the original trilogy did better than the prequels. We didn't need backstory about trade federations or midiclorians or the workings of the senate, we just needed to jump into the story and figure out what was going on.
The real question is, do the loose ends and/or plot holes matter? Rey has spent her life rummaging around in old space ships and she knows how to fly. Is it really out of the question that she might know how these things work? She learns how to use the force quickly. Luke got pretty good with the force even before his training with Yoda. Also, she seemed to get better with it after each encounter with Kylo Ren, so in a way he was her teacher. You know who also was good at fixing things and learned how to use the force quickly? Luke and Anakin Skywalker. Does it ruin the movie if she's not related, but just a quick study that's unusually strong in the Force?
If I'm looking for a real plot hole, how in the world does anyone have a map to where Luke is? Particularly, how is most of the map contained in records from before the fall of the Empire? This is the MacGuffin, of course. We need a thing like the plans of the Death Star to find and/or keep from the enemy. Still, its existence makes absolutely no sense.
Might I be forgiving some things here that I would pick on in the prequels? Perhaps, that's difficult to judge. But here's the thing, the prequels were awful movies, regardless of these things. Forgiving them wouldn't have made them good.
Does this film serve as the first act of a trilogy? Absolutely, but I also think it works on its own. Even Episode IV had Darth Vader speeding off into space. I can recall my father, immediately after exiting the movie theater from seeing Star Wars the first time. "We'll see him (Vader) again." Likewise, we'll see Kylo Ren again, though I found him one of the less interesting aspects of the film.
BTW, if you're looking for a fairly comprehensive list of questions raised but not answered by The Force Awakens, have a look here:
http://io9.gizmodo.com/33-questions-we- … 1748953034
I don't expect all of those questions to be answered, but I'm betting some of them will. Some of them are, I think, already answered in the film in one way or another. If they aren't, though, does it really matter?