Regarding Forge ghosts. Here's Obi-Wan from the OT:
Yoda in TLJ seems well within the range, to me.
Regarding Force ghost capabilities. I said it in a spoiler tag some pages back ,but I'll repeat it openly here. In Star Wars, Obi-Wan told Vader that if Vader struck him down Obi-Wan would become "more powerful than [he could] possibly imagine." Some attribute this to the psychological impact of Luke seeing Old Ben killed motivating him. Lucas originally intended something more tangible. Obi-Wan's progression from disembodied voice to hazy, distant figure to near and close -- but still static -- figure to being able to move around, push vines aside, and sit on a log to talk to Luke were part of a deliberate progression. In early notes, he was going to step back across the veil to corporeal form to help Luke defeat the Emperor at the climax. Later, Lucas decided this would undercut Luke's victory (and I feel he's correct in that). One in-universe rationalization for that not happening has been that the Emperor's aura was too strong for him to get through to help. My preferred take is that he just hadn't had enough time to finish pulling his residual self-image into sharp enough focus. Being able to bonk Luke on the head seems well within the bounds of what Yoda would be able to do so long after
he merged with the Force. And, since he's Yoda and this was a Force nexus, I have no problem with Yoda being able to call down the lightning.
I'm still holding out hope that Obi-Wan, Anakin, or even Luke might appear. To Rey or Ben or both.
Now, for the story as a whole...
I am one who feels it should have been two episodes, but I also feel the Prequels and OT should have been six each, include Rogue One in there, and have done a lot of sloppy recutting to see if the story actually works (it does), and, if so, if it works better (I think so, and so do the people I've shown or told, for what that's worth). I've only seen TLJ once so far, but intend to go back at least twice more. Most of the story elements work for me. I've already done a quick-and-dirty re-shuffling and re-contextualizing that improves the presentation, but leaves us at the same point. Which is one I like.
For who only knows how many thousands of years it's been Jedi and Sith, Republics and Empires, Dark rising and Light rising to restore balance, Light rising and Dark rising to restore balance, round and round, with billions dead along the way caught in the crossfire. The whole point of this movie is "It hasn't worked, no matter how often it's tried. We gotta do something new." Who Snoke is doesn't matter, except academically. He's a symbol of the old and well-established cycle, and thus a symbol that has to be destroyed if we're to move forward. It's exciting and scary because we don't know what that "something new" will be.
One thing that
is clear is it won't be the old post-ROTJ EU, with repeated happily-ever-afters that end up not sticking because the newest superweapon of the week or Emperor-Wannabe comes along to keep things in turmoil. Peace is boring. Can't have movies without conflict. I'd rather have conflict that moves the story forward rather than keeping it locked in the same endless cycle of Jedi vs. Sith. My biggest gripe with the new films (besides that there need to be more of them to let the story evolve at its own pace) is JJ's frikkin' Mystery Box. We needed more at the top of TFA. We needed more tidbits. Not a lot, but more than we got. It would have made it easier to accept that Our Heroes are older and have reacted all-too-humanly to things not turning out as they'd hoped.
I keep thinking of a couple things from the Nolan Batman films. "Die a hero, or live long enough to see yourself become the villain." This may not be the Star Wars we want, but it may end up being the Star Wars we need.
--Jonah