Lost has basically back to what Lost was, but with a group called The Others (who is lead by a *very* weird man...if you ever watched Without a Trace or The Practice you might have seen him guesting on those shows...he's got really big eyes and just looks scarey!). To pick up where you left off, the hatches are no longer in the picture...although Desmond (the man in the hatch) is on the show now. He was actually the one to cause the plane to crash, because he didn't push the button in time, and it caused an electromagnetic field, which threw the plane off course and causing it to crash on the island. Michael made a deal with The Others and they gave Walt back to Michael and let them go home. Jack, Kate and Sawyer were taken by the Others and held hostage...they put Sawyer and Kate in cages and forced Jack to operate on the leader (the very weird guy), who had a tumor on his spine. Sawyer & Kate managed to escape, the leader recovered, and Sawyer, Kate & Locke went back to rescue Jack. They got him back, but they had to agree to bring Juliet (another of the Others) with them. She wants desperately to get off the island, but the leader wouldn't let her go, and was ordering her to do tests on any woman on the island who is or could be pregnant (Sun is pregnant). She told Jack what was going on and that she wasn't going to follow Ben's (the leader) orders, but none of the other Lostees knew that.
In the meantime, a parachuter showed up in the woods...she claimed she was sent by Desmond's girlfriend...but in the final episode, we found out she wasn't. Charle & Desmond made their way to an underwater hatch that was blocking the radio signal. Charlie was able to flip the switch and he got a signal, and on the other end was Desmond's girlfriend. When Charlie told her that her parschuter had landed on the island she was like "I didn't send her". This switch was in a small room with a door. A Russian 'Other' had a grenade outside the porthole of the room...Charlie was inside, Desmond was outside...Charlie closed the door, the grenade went off, and Charlie drowned.
As for the flashbacks, the season finale turned from flashbacks to flashforwards. It starts off with Jack wanting to commit suicide...at first the audience thinks its a flashback, but then later one we find out it's a flashforward to events that happen after they get off the island. A lot of people seem to think that from now on, the island scenes are going to be the flashbacks. At the end, Jack & Kate meet up...Jack says to Kate the he's been trying to get back to the island (the airline gave all the survivors free lifetime passes to fly anywhere), hopping flights hoping one day another plane will crash in the same place.