If you think Radcliffe's acting is so awful how can you possibly think that he'll be fine for the next two films when they're going to demand so much more from him? Harry's character is far more complicated than just being arrogant and even if it wasn't you'd still need a good actor playing him. IMO Radcliffe's improved a lot and I now enjoy his performances, but nevertheless I'm worried he's not good enough to pull off Harry in Order of the Phoenix, it's a difficult role that even the most blessed actors would find taxing.
While I'd agree that Grint is the most natural actor of the three, he's far from brilliant, he's become very overrated as people have leaped on the 'he's the true talent' bandwagon when, in my opinion, I haven't seen anything overly impressive from him. Maybe my opinion will change when I've finally seen 'Driving Lessons,' where he's apparently given the opportunity to show more range.
Watson neeRAB to be told to reign it in a bit, she overacts but i do think she's got talent and thought she was good in the third film. Calling her 'wooden' is ridiculous. I'm annoyed that people are accusing her of trying to get more money, she explains in the interview that each movie takes a year to do and while she loves acting she also loves a lot of other things which she wont have the opportunity to do while tied to such long shoots. She's a very clever girl and there are more important things in life than being famous and rich.
Basically I think all three of them are pretty good but would benefit from some acting tuition which they probably don't have time for at the moment.
The young supporting actors are good but you must realise that they don't have the demanRAB on them that the trio have.