The Mario cartoons were perfectly fine if you ask me, with the exceptions being the ones that parody fairy tales and stories, like where Bowser dresses up as Captain Blackbeard, Attila the Hun, and etcetera, which are really cheesy. The ones that don't focus on those parodies are fine. They were goofy,funny, and lighthearted, which is what Mario is. Suddenly making some dark edgy Mario cartoon will end up causing it become like Sonic the Hedgehog has in recent years.
Would a Mario cartoon work these days? I'd say no. Very few video game cartoons do these days (most being made in Japan these days, and only one or two actually being worth watching) It worked in the past since on 8bits systems, there was no dialog, no real story, just get to the end of the level and beat the boss. Samething with the Zelda cartoon (though surfer Link is cheesy, Link had no personality in the games back then. Heck, he still doesn't have one since he never talks, which is why I think a Metroid cartoon wouldn't be good.)
Granted, Mario and Zelda still don't have as deep or intricate stories like an RPG or anything, but I think companies have realized cartoons based on video games don't work out in the long run, especially if it's a well-known IP. People enjoy the games so much because of the gameplay, not the story. This is especially true with games with extremely simple/no stories, like Mario.