A few thoughts:
No, they were not dead the whole time on the island. I've been hearing, and reading, a lot of people saying the Losties were dead and this was purgatory. No. Go back and watch the finale. Listen to Christian in the church. He says they built this place (church) to find each other. Basically, they made such deep connections on the island that they all met there when they did die so they could move on together. The whole sideways world was a kind of purgatory, I guess, where they found each other so they can meet at the church.
Part of the problem I think some people had was the timeline. The meeting at the church was not really happening right after Jack died. Hurley and Ben let you know that when they tell each other how good of a job they did on the island when Hurley was running things. Also, Sawyer, Claire, Kate, Miles, Lapidus, and Richard all made it off the island to make a life for themselves for a while. How long? Who knows. It doesn't really matter. Their story ends after they leave the island for good.
What was the deal with the light cave, the hieroglyphs and all the weird stuff like that? I think that was just to let us know this has been going on a long time. There has been a protector of the island for ages. Why? Again, that's not the story. The story we are being told is of the people on the island this time around. The story is how these people, who are lost and alone in life, make connections that last a lifetime. And beyond. The island is just a secondary or tertiary character at best. At the same time, I did like all the skeletons that were found in the glowy cave. Obviously people have tried the same thing Jack and Desmond did in the past.
In short, yes, I liked it. For a show like that it's about the best you can hope for. But, I'm not a TV critic. There are many other people out there who can give a longer, and deeper, discussion of the finale.
But, I didn't have an idea for some spin-offs. Ready?
Smokey and The Bear: Follow the smoke monster and the polar bear as they travel the island to look for innocent people to scare to death all through history. Good times. I would only expect this to last one season. Maybe half.
A*F*T*E*R*Lost: Follow Ben and Hurley and as they wander the island to find people to help. It's a new regime, people. As castaways wash up on shore, Ben and Hurley treat their injuries (with Ghost Jack's help) and help them build rafts to get off the island. Special guests to include; Donnie and Marie Osmond, David Hasselhoff and a special appearance by the Harlem Globetrotters.
Sawyer, P.I: This is perfect. Sawyer is a PI, Ben is the stuffy, uptight caretaker of a mansion that Sawyer get's to live in for some reason. (Yes, Ben would be on two shows. I don't expect A*F*T*E*R*Lost to last long). Along with his buddies; helicopter pilot Lapidus, slick restaurant manager Sayid, and police officer Miles, Sawyer helps people with their problems. Usually the problems will involve solving a murder, or preventing one, and stopping drug traffickers. Hey, it's not the 80's anymore. Occasionally, Sawyer's long lost love, Sun, will show up on the island. She can't stay and leave her family behind, but she still loves him. Come on, who wouldn't watch this?
Two Girls, a Ghost, and a Baby: Kate and Charlie's ghost help Claire raise baby Aaron since she is a little nutty for a little while after coming home from the island. Oh, the fun dates Claire will go on and while she's still crazy lady. It will be great!
That's all I can come up with right now. Let me know if you think of any.