( Warning: Very vague spoilers for Arrow and Once Upon a Time ahead. )
I really like having flashbacks in a TV series. Whether it be a single episode where we get into a character's backstory/origin or a show entirely cut between the past and the present like LOST. There's just such an added thrill for me when I start seeing connections between what a character does and the motivations of their past. Especially when we get into superheroes with their assorted origins.
I've noticed that when a TV series is based very heavily on flashbacks, there are usually one of two ways that they go about it.
The First Method: Random flashbacks that are shown as they become relevant to happenings in the present.
I am currently watching the ABC series Once Upon a Time and it fits well into this category. We start off with the Evil Queen making threats at Snow White's wedding, then jump back to her hunting Snow down in the woods, then the huntsman first hired to kill Snow, and then into the first time Snow and the Queen met. Obviously, these events are being show out of chronological order, but they are always relevant to what is happening in the present storyline.
Evil Queen and Snow White's first tragic meeting in flashback = Snow asking why Queen hates her so much in later episode.
With this method, things are dredged up from the past as they are needed. After a long while you get a sense of just how things played out in the grand scheme of things, but it can become a chore to puzzle it all together. Though that can be part of the fun as long as the audience doesn't get the feeling that you're making it all up as you go, which I have suspected of Once Upon a Time.
The Second Method: Chronological flashbacks that just so happen to align with current events.
I am also watching the CW series Arrow and it really introduced me to this method of past and present running alongside each other. This first episode shows Oliver Queen being rescued from being marooned on an island in the present and then shows how his ship wrecked in the first flashback. From then on, the story is pretty well locked into both past and present flowing at the same rate. As Oliver becomes "the hood" or "the vigilante" he's essentially a savage killer bent on saving the city from itself. This is well balanced by the flashback to the spoiled brat that was marooned on a hellish island for 5 years becoming more and more bent on the idea of survival at any cost. You get to see Oliver come unwound in the past as you watch him try to hold it together in the present. This provides such a great parallel.
A good friend of Oliver's dies on the island in a flashback = Oliver survives a near death experience in the present only to be haunted by said friend's ghost.
With this method, there is a huge element of predictability involved. Like, we know the latest "Get off the island" scheme is doomed to fail because he has to be marooned for five years to get to the current storyline. But the amazing thing here is when the writer's can still surprise you with certain things that unfold, even when they've revealed so much to you already.
I personally like Arrow's method a bit more than Once Upon a Time's. Mostly because TV series in general have this notion that they have to go on forever and ever and only end up losing their charm (Supernatural and Stargate). However, I know that Arrow's story must have a definite conclusion because after the 5 year span is up, we'll have caught up to the present story.
With the random flashback method, you could very easily say that this out of the blue thing that supposedly happens between two other points was totally part of the continuity from the start (like Tinkerbell and the Evil Queen being pals) and it might totally be true, but after a while I start to wonder doubt that.
With the chronological flashback method, I may know right off the bat that certain things are going to happen (like everyone has to die because Oliver was rescued from the island alone), but there's a great sense of continuity that comes from being able to predict some things and feel that the story can't surprise you. And Arrow still manages to surprise me every season, so that whole feeling is probably a bit presumptuous anyway! They're just lulling you into a false sense of security!
That's all for now. Thanks for reading! TTYL.