I checked out 21 and thought it was enjoyable. It would be a good one if it is on TV and you can record it to your DVR. It is about a brilliant student (Ben) at M.I.T. in Boston who wants a scholarship to go to Harvard Medical school which Ben can't afford. He is introduced to a small group of M.I.T. students that count cards in Blackjack which is lead by one of his professors. They spend their weekends being high-rollers in Vegas and then the rest of the week studying for school in Boston. Ben shows he is the best of the students and leads the time to take a lot of money from the big Casinos. Laurence Fishburne is a ruthless security consultant that wants to take the team down. He beats people to a bloody mess to let them know that they shouldn't cheat.
It says the movie is Inspired by true events so I looked into that, seems that the only true thing is that MIT students counted cards and made lots of money. Everything else was added to make the story more interesting. Also the team was mainly Asian so that made people upset when the main talent wasn't Asian.
"Bringing Down the House" by Ben Mezrich (same guy who wrote "The Accidental Billionaires" which was turned into The Social Network). It's a great book with more suspense and intrigue than the movie, in my opinion. If you thought 21 was mildly entertaining, you definitely need to check out the book.
But to contribute a nugget to the conversation, I don't know if I ever plan on seeing 21, but I do like Rounders. I just watched part of it the other day, made me want to go back and watch the whole thing again.