Yes, it should have been a process. I admit that they did not illustrate that transition from wonderment to comfort (well, even in book four he's still in amazement, and sort of naive about it all) very well. However, people who have read the books, it seems (I should know, I'm among them), just fill in those gaps, seeing as how they read them already.
What gives? They're kids! Kids want to win. Kids love that kind of stuff. In the book, Slytherin is played up more as the most despised house. In the movie, you get one line to hint at it: "There wasn't a bad witch or wizard that didn't come from Slytherin." In the book, this is expanded upon: they're very ambitious, but, as a result, more of them go astray. They've also won the House Cup many years running...in the book, when Gryffindor finally wins it, it almost makes a new era. They have a famous, talented student on board now, and are, in a way, starting a dynasty of their own. This is minor stuff for the movie, though, and I don't blame them for cutting it out.
And yes, that is the way they are...no, it does not make up a story...the story stood on it's own without it.
What motivated his quest? Wouldn't YOU be curious about that object? I sure as hell would...and I'm not 11...when those kinds of things are at their most interesting. Anyway, another note: in the books, they're off doing other things in the background, which is really more realistic. Real kids would get into all kinds of trouble, or have other "things" going on...in the movie, there isn't time for more than one or two of those subplots.
I thought it was an amazing movie. It has some great lines, some great symbolism, and is based on a great story. It's not perfect...but then again, you can't expect it to be. I think the majority of negative reviews are the result of expecting it to live up to unreasonable hype.