I think one of the underlying themes of the show is that everyone has secrets that they carry around with them and keep at a distance from other people. Furthermore, it's these secrets that make people who they are. The show then is about the breakdown of this distance by forcing these people together in a hopeless situation. Therefore, in order for the show to be character-driven, it's important to reveal these mysteries. Now, in some cases they are twists, true, though in some they aren't, and which are which I'll go into below because I have more point to make.
The flashbacks serve not just to reveal mysteries about characters
(who they are)
, but to show
why they are the way they are. In contrast, we have the present, where we see not just who they are, but how their secrets affect not just them, but those around them as well. Tonight's episode was an excellent example - Sawyer's (who I believe said his name was Nate) persona doesn't just affect him, but it affects Kate, it affects Sayid, it affects Jack, it affects Boone's sister (what's her name again?), and so on. Furthermore, sharing the secret of his past allows him to move on and change... something that hopefully we'll see in the coming episodes.
Assuming Jun couldn't speak English because she hadn't yet doesn't mean the story was a twist, it means that there was stuff about her we don't know, and neither did anyone else. The writers did try to make it seem that Sawyer was the criminal instead of Kate, but they played on the tendancy for people to judge a book by it's cover, so to speak. Thus we go back to the premise of the show - that everyone has secrets, and while in some cases they're relatively normal (Charlie, Jack), in some cases they are exceptional (Sawyer, Kate, Locke). Just because you
think you know someone, doesn't mean you do, and that's one of the big points the show tries to make. It goes right back to the pilot, when Hurley assumes Sayid fought for the US, because Sayid was a nice guy.
One note, the only story I think was deliberately twistful was Jack's, and thus it makes it hard to judge Jack's story. Really, Jack's only secret is that his father died, and maybe he was emotionally abused as a kid. That's not particularly twistful... in fact, unfortunate as it is, it's a relatively common story.
Also, it's hard to judge the show's form based on only seven episodes. Keep in mind that they do want to keep the show on the air, and people with normal lives are generally pretty boring. That's why we only see the stories of a core group of people. Few people want to see the flashback of how Jack performed a routine spinal surgery. Also, the show wasn't picked up for a whole season until after it became a hit - these first few shows (seven out of twenty-one, I believe) have to grab attention. As a poster (I forget the name) wrote in another thread about a movie, (paraphrased) if it doesn't have enough twists, it's not as good a movie as one that does.
As a final comment, it's readily evident that this show is about the characters and not about the mystery of the island. Anyone expecting an X-Files type show (which was more formulaic than Lost, IMO) will be sorely disappointed. It's been stated in interviews that they intend never to fully reveal what the monster is, or all the secrets behind the island. There will be allusions and there will be hints, but never the full story, because it can not compare to what we build up in our minds.