Easier just to list my responses:
1) The "whys" and "wherefores" are pretty simple: can someone play a variety of rolls where they show that they're not just playing the same thing over and over again? The perfect example of a great actor is Gary Oldman. Most of his rolls you can hardly tell it's him, like Dracula or True Romance. And even when he plays the "straight" guy, like he did in The Contender or Batman, they're still very different. Even Pacino or DeNiro, when he cares to challenge himself. Unfortunately, that's happen very rarely other than the late 70s, early 80s (Godfather, Taxi Driver, Deer Hunter, Raging Bull) and then again in the early 90s (Goodfellas, Awakenings, Frankenstein). Other than that, he's just accepted the money that comes with his typecasting but that don't mean he ain't a great actor like he's showed in the past.
Then you get guys like Keanu Reeves, Bruce Willis, DiFaggio, or Asscrack. They are pretty much the same character/person in every film they've done. That don't mean their films suck (well, in Asscrack's case, they pretty much all do except for Gone, Baby, Gone; and no, I didn't like The Town) but the films certainly aren't made better due to their performances. They're little more than plugs. There's a specific performance they can deliver and it fits the movies they're in. The first 3 have been in some of my favourite films of all time (Matrix, Die Hard, Inception, Titanic just to name a few) but I don't consider them to be great actors, none of them. They don't drag films down due to their performances (unlike, say, Asston Kutcher) but they don't enhance them, either.
2) Yes, very serious. Michael Keaton is a MUCH better actor than people wanna give him credit for, kinda like Brad Pitt. They're not in the upper echelon like Oldman but they're significantly above the plugs like Reeves or Willis. And he has, at this point, delivered easily the best Batman on-screen that we've seen. It's not even close
Asscrack has never surprised me with his acting ability....ever. His best rolls are in Kevin Smith films and that's because he's hammin' it up with Damon and Smith uses them well. I've NEVER liked his acting ability and he has never given me a reason to change his mind. He should just stay behind the camera, he's better there.
Eisenberg is a plug. Cera's act is old
3) Yes, banned. Paycheck (2003) was the last big-budget film he was in. Since then, it's been a series of dramas and directing gigs with Oscar noms to get back into one for next year. That's 11 years, that's being banned. And look at the HUGE outcry that's happening because of it. People haven't forgotten.....
4) Yes, his mouth. When Christian Bale smiles or even talks, his mouth looks a bit odd. It's very distinctive but not necessarily in a good way. Considering that's all you see of him for half the film, I found it an odd choice. His performance as Batman (sadly, second-best behind Keaton; although I do have a soft spot for West) never redeemed him like Ledger's did for the Joker
And for the record: I'm pretty neutral on Bale in general. He just wasn't right for Batman
I was there on that fateful day, were you?