There's lots of coverage of news that the 9th US Circuit Court of Appeals has struck down California's legislation which tried to restrict the sale of "violent video games" to minors - in the spirit of the media hysteria which accompanied Barack Obama's visit to Ottawa this week, let's try for a Canadian angle, shall we?
Many Canadian provinces have similar legislation in place which seeks to prevent minors from purchasing violent video games, none of which, to my knowledge, have been successfully challenged in court. There are, however, structural differences in the US and Canadian legislation which are likely material to any potential court consideration.
Here is the text of the original California bill. Here is the 9th Circuit Court of Appeals decision in Video Software Dealers Association v Schwarzenegger. Ars Technica has a series of detailed posts covering the bill and the history of judicial action against it (in reverse chronological order) here, here, here and here.
And here is the comparable Ontario regulation (under the Film Classification Act, 2005), which makes it illegal to distribute or exhibit a video game which has been rated "Mature" to anyone under 17 years of age (see section 6(2)) and also illegal to distribute or exhibit a video game which has been rated "Adults Only" to anyone under 18 years of age (see section 6(3)).
The primary distinction between the two pieces of legislation relates to who makes the classification. In California, it would have been (the bill was never actually enforced due to the court challenges) the government itself making the decision - in Ontario, that task has been delegated to the Entertainment Software Rating Board, which is an industry association. The California bill contains rather extensive definitions of terms such as "violent video game", "cruel" and "serious physical abuse" which are intended to guide government bureaucrats in making classification decisions; the Ontario regulation defers the entire exercise to the industry association. Freedom of expression doctrines in Canada and the US are... perhaps not "radically" different, but certainly different enough that making comparative guesses in situations like this is exceedingly difficult - that being said, I would be surprised if a Canadian court concluded that the existing regulations violated the Charter.