While Sony doesn't have a Mario, they had the chance at two Marios (Crash and Tomba). A series like Halo could be fashioned to appeal to kids in the same fashion that Teenage Mutant Ninja Turtles (which was a more mature series), Inhumanoids (which was mature for its time), Mutant League (which was graphic for its time), Toxic Avenger (mature in content, but mainly EC Comics-grade mature), and Mortal Kombat.
All of those were mature in content but managed to crossover up until it came to making the connection between the kids audience stuff to the teen/mature audience. While TMNT had the longest run and could've easily bridged things the comic had finished up by that time and MK was popular on the myth of what was MK. The cartoons and TV series made it easier to consume if parents weren't allowing kids to play the games.
Nintendo didn't have the younger market until Sega Mega Drive came out with the American advertising of the Genesis. Before that Nintendo was the market. It was just a gamers' market. While things were colorful and could've easily been advertised towards kids, those same products had the gameplay to draw in hardcore gamers with the difficulty and challenge available.
That's something only Sega, Nintendo, and some of the earlier studios could do: make games that appeal to everyone in one package as opposed to making a game for "mature" audiences with blood, gore, scantily clad women, and swearing (which is more of a teen game actually, the maturity should come in with a storyline) and another game that is pretty dumbed down and colorful for kids.
And Halo is a heavily action packed sci-fi shooter. That's would be prime crossover material for everything. The thing that makes it firmly mature (aside from the storyline) is that it's a FPS and those have been typecasted as being M-Rated games even though plenty of them are only that because of blood, realistic weapons, the language, and human-on-human violence.