JJ and his “mystery box” approach worked for getting people interested in the “fresh start” aspect. However, without any actual payoff, TLJ retroactively undoes any intrigue or mysteries of TFA. The surprises of Empire don’t make watching ANH worse in its plot points (for the most part) but TLJ makes all the questions from TFA basically pointless.
They were dumb questions to begin with.
Rey’s parents was kind of interesting but when you don’t answer it and leave us to think about it for a year, then everyone forms clear ideas on who they think they should be (lucky me my theory was correct (until TRoS)) and get disappointed when the reveal isn’t what they asked for. Would the Vader twist in ESB have had anywhere near the same impact if ANH had spent its runtime poking the audience to ask who Luke’s father is? No, because we would’ve seen it coming a mile away, while some fanboys would ramble about how Obi-Wan or Tarkin should’ve been his father instead.
As for everything else, I’d argue it’s less intentional mystery and more Abrams stumbling over his own feet by skipping any kind of backstory. Did you really think Snoke was supposed to be someone we knew? Of course not, because he was just Palpatine 2.0. What Abrams failed to realize was that unlike in ESB, you can’t just introduce the evil ruler of the universe without providing some context. Naturally, people started asking questions about him.
Same goes with the Knights of Ren. From their first appearance in TFA I knew exactly what they’d be and I was right. They were Kylo Ren’s personal extras, with one or two fight scenes, no lightsabers even though they should have them, then they die. What you expected an explanation? You must’ve forgotten who’s making these.