First off, M. Night Shyamalan's last couple of movies weren't so great, but his track record isn't awful. It's not like Michael Bay or even Uwe Boll is making this movie. It's being made by a director who knows a few things about actual storytelling, and doesn't use special effects to cover up shoddy direction. The guy made Unbreakable, and with that in mind, I'm willing to give this movie some latitude on the outset.
Secondly, casting wise, people need to cool their jets. It's not the first time casting choices have gone this way. Besides, it's not like anyone in the original AMERICAN MADE cartoon blatantly stated that they were Tibetan, Chinese, Japanese, or Caucasian. Shows like that tend to leave genealogical concepts ambiguous. Get over it. Hell, we don't have ANY idea how this main kid is gonna go, being that this is his theatrical debut. We have seen absolutely no shots of anyone delivering dialogue. Who's to say that the acting will be bad? We have absolutely NO grounds to assume the acting will suffer. It's a nitpick that has no bearing on the quality of the movie.
Finally, why build any expectations on movies like this? Hope that it's good or bad, but to expect anything is dumb. M. Night is gonna make this movie, hopefully to the best of his ability. It turns out how it turns out. It could end up blowing you away. I'll be the first to admit that anime (inspired, in this case) turned blockbuster tend to end up crap, but to say that based on history that this movie will definitely be horrible is a faulty syllogism. All you have to go on is a trailer, and this trailer had the kid, and a bunch of ships. That's it. This isn't Dragonball. This isn't Transformers. The circumstances for this movie are wholly different than any beloved property turned movie before it.