[Over]

I wouldn't like a new Lost series or movie. It endend very well, the most important things were explained, it had an excelent emotional impact (all those tear-jerking reunions helped). There are holes, but I wouldn't say those are huge holes. We never get a full picture from life, just our point of view. The series was based on the losties (those who were on Oceanic 815), and specially Jack. There are some holes because they didn't get to know everything. Even fake Locke and Jack didn't know exactly what would happen in the end.

About Ben:

Spoiler:

I think he didn't enter the church, because he wasn't connected to those inside. He is living his "purgatory" with another set of people important to his life, like Alex, Rousseau, etc. When they "remember", then they can move on from their special place.

About the sideverse:

Spoiler:

We all can agree that the island was real and that what happened there, really mattered, just like Jack affirmed. The sideverse was some kind of purgatory. There's no "here" or "now", like Jack's father said. It's somewhere in the future when all those in that church were dead: some before Jack, other after (those who escaped in that Ajira plane) and Hugo probably centuries later).
The purgatory was a place where the characters get the opportunity to attone themselves, then finally remember who they are and then finally move on.
Sawyer was a con man, here he's ironically a cop. Jack get's the opportunity to be a good father, Ben gets to be a more selfless guy and a better father figure to Alex, and so on...
Locke has forgiven Ben before entering the church. Ben said it really mattered and we know why: he hasn't been a nice guy. This forgiveness plus his actions in the purgatory and a good job at helping Hugo protect the island will certainly allow him to "move on".
Michael didn't pas the island's test. He made very bad choices, he murdered and never got to redeem himself. That's why he wasn't allowed to go to the sideverse. And that's why he wasn't in that church and moved on with the rest of the crew. He also never did connect with them, so even if he attoned, he would never leave with them.

An excelent series, that could have skipped a couple seasons. If a movie appears, I probably wouldn't resist to watch it, but after 6 yeras, that's almost 10% of our lives. A lot of time together. Lost should RIP, allowing us to move on too.