I think it's fair to criticize JJ for his flaws, and the man does have them as a storyteller on both the small and big screens.
JJ's biggest flaws, as I see them, are:
1. He looooooves crafting a mystery, or at least raising questions in the audience's mind. The thing is, sometimes I think these questions are unnecessary to the story you're trying to tell, and sometimes I think he doesn't actually know the answer to the mystery. It's a great way to build excitement, but I think he sometimes leans on that trope a bit too heavily (e.g. "Is Cumberbatch Khan?" "Is the island just purgatory?"), and can often fail to deliver with the big reveal. In this case, though, I suspect that they've already mapped out Rey's journey, her backstory (which is the mystery the audience currently faces), and know how they're going to get from A-to-B-to-C with it. In a way, it's less a true "mystery" and more just "information that hasn't yet been revealed to the audience."
Mostly, I believe this to be the case because TFA -- and Star Wars in general -- is no longer the work of a single auteur, subject to such auteur's whims. Lucas threw in the "No. There is another..." line in ESB without really knowing who that other is. He made Leia Luke's sister so that Luke would have a reason to go nuts when Vader threatens to turn her in ROTJ (without regard for the previous romantic tension he'd laid out in ANH and ESB). He made it up as he went along, basically, and changed his mind at times, too. That's not likely to happen with the new Star Wars material. First, you have the Story Group riding herd on what's being told, and second, with a mix of directors, you don't have the entire story subject to a single director's whims. The stories are being developed collaboratively. That means that for the next person to step in and take over, they need to know the direction they're supposed to go. How they get there may be up to them, but the direction is pre-determined.
2. JJ has blindspots in storytelling and/or allows other people involved to let their blind spots go unchallenged. As a director, he sometimes seems to (erroneously) assume that the info is all there for the audience to see,or simply thinks that some info isn't important when it is. Case in point, the whole issue with the difference between the Resistance and the Republic, and the 30 years of backstory. There may be some 400-page version of the TFA screenplay that includes a mass of scenes and exposition that were cut or never filmed at all, which lays this stuff out. But the film, as shown, is missing a LOT of backstory, and it leaves folks confused. This is doubly problematic when you have the "competing narrative" of the EU, which was allowed to exist for 20 of those 30 years, and then was summarily fired out an airlock into "Legends" continuity. With this Chewie thing, JJ probably just...missed it. It was a mistake. He didn't read how the scene would play to certain audience members. It just...never occurred to him. Now that he's been asked about it, he recognizes the mistake, and has a reason for why it was shot that way, but...yeah. It's a mistake. Due to blind spots.
3. JJ has a short attention span. Rather than craft a long, overarching narrative, I think he's a lot closer to, say, a Spielberg who wants to just tell a story and move on. Spielberg isn't making Minority Report 2, or War of the Worlds: Aftermath or whatever. Aside from the Indiana Jones films, and maybe a production credit on Jaws 2, Spielberg has largely just done standalone films. JJ, to me, is far more like that. I think it's hurt him in his TV endeavors because he just...you know, gets bored and wants to move on. I don't think he's as good as young Spielberg is (because almost nobody is), but I do think he's on par with the Spielberg of the last, oh, 10-15 years.
As for JJ's derivative approach, I mean, folks, we're talking about the Star Wars franchise. The whole thing is derivative. Lucas literally lifts shot compositions and lines of dialogue from several other films in ANH alone. Stylistically, he's just telling a Buster Crabbe Flash Gordon serial, mixed with western elements, and a few Kurosawa and jitai geki references thrown in. Is JJ derivative in his style? Absolutely! But...so what?
