I think it's reasonably fair to say that, from the show's inception, the flashbacks were among the weaker elements and that, as time went by, they became increasingly redundant. (Yes, yes, we know: Kate has to "escape"; Jack needs to fix things; Locke has daddy issues, etc.) There were exceptions--notably, a few of the Hurley flashbacks that were penned, I think, by "Angel" veteran David Fury--but, watching the show, I know I wasn't alone in typically rooting for the flashback scenes to conclude quickly so that we could return to the main storyline.
It's obviously (very, very) early, but on the basis of last night's season premiere it seems as though that preference could easily flip. The flash-forwards that the show (brilliantly) sprung on us at the conclusion of Season 3 and that continued last night are, at the moment, its most fascinating element. Partly, this is because "What happens next?" is almost always a more intriguing question than "What happened already?" Partly, it's because the regretful tone of the flash-forwards gives the show a darker, more somber resonance. And partly it's because the mysteries on offer--who's in the coffin? who are "the six"? what's the implicit deal Oceanic seems to have made with them? how is it that Charlie's come back, and why does he look so much better than he did when he was alive?--are just so damned tantalizing.
Emily Nussbaum has a much longer, and characteristically fun, rundown of the premiere over at Vulture. But, from my point of view, this was a very promising beginning.