If you're right about it being Michael, then Walt probably didn't show up because he learned about what he did to get them off the island (killing Ana-Lucia and Libby and such.)
As for Walt, I doubt that was actually him. Here's MY crazy ridiculous theory about it all. Jacob and The Smoke Monster are not one and the same, but they are indeed closely related. Jacob can shift shapes and stuff, to communicate with people. This would explain Christian, Kate's horse, Walt, Yemi, and all other similar stuff. Jacob usually takes the form of someone the person knows or knew. So that way, Locke won't be all "Wait, who are you?" and go crazy and set fire to him, he'll think it's Walt. Wouldn't want to set fire to Walt. Same thing with Yemi and Eko. JacobYemi lured Eko into the jungle to have Smokey unleash hell.
I agree about Jack's dad, he was probably just drunk. When he said "upstairs" he probably meant Heaven or something.
And, yeah. Charlie's death made no sense, kind of. I wonder why he didn't go through the window or run out the door before everyone's favorite Immortal Cycloptic Russian Other Guy, Mikhail, blew up the window.
I burst out laughing when Hurley came in with the van. I forgot about those vans! I figured Hurley would stumble across something AMAZING, like Jacob's Secret Lair, and the camera would pan around to his face and he would say "Woah" or "Dude". But this works too.
FINALLY! I hated the flash "backs" until I saw the last one. I mean, bla bla bla, Jack sure was pathetic, come on let's get back to the island grrrrrrrrr. Now the flashforwards seem so much better now. I also hope that all flashbacks will be replaced by flashforwards, because there's really not much left to tell in them anymore. Although it could get confusing (as if it isn't now...)