I don't want to give spoilers, but I don't know how to implement a "Click here to read more" in this environment. So if you're planning on seeing the movie 21, don't read the following...
OK I enjoyed the movie but only because of the subject matter. I actually thought it had several serious flaws. Among them:
(1) That kid couldn't act very well.
(2) All of the exposition. Give me a break. My wife pointed out (in regards to a different movie) that movies always do a dumb job of portraying geniuses. For example (back to this movie), would Kevin Spacey's character have spelled it out so sloooooowly when quizzing the kids in their secret room about what the count was? No, he was clearly just reiterating how it worked for the benefit of the audience. And when the kid first plays at a live table, and you're in his head? Give me a break, he wouldn't have been spelling out the rules like that.
(3) Near the end, Laurence Fishburne's character is both driving the limo with Spacey, and is right there to rip off the kid and his girlfriend when they pop out of the building. Those two kids must have been one or two minutes behind Spacey, tops. So even if you give me a JFK-style story about how this could be physically possible, I don't believe Fishburne would have taken such chances with his retirement on the line.
(4) The movie gave the impression that once given the signal to sit down at a hot table, the high roller would stay there for a while. Clearly he was there through a shuffle. Yet Spacey yells at the other high roller for missing the signal to leave and playing three times "into a cold deck." So what's the deal? Do the high rollers get up when the count goes negative or not? The shoe can't stay good for as long as it portrayed them sitting at the table. It evens out by the end, which takes about 15 minutes, and even less if there are only 3 people at the table. Plus the high roller wouldn't sit down until the shoe was +17 or so, which means the shoe was probably half gone at that point. He'd maybe get 5 or 6 hands in, and then have to switch tables.