Metroid other M, new trailer.

[Majin-Tenshinhan]

Demotruk said:
What does "main series" even mean? There are bigger series, and there are smaller series. Metroid is certain not one of the bigger ones (though it's not exactly tiny either). 2.8 million is the top selling Metroid game, which pales in comparison to many of Nintendo's franchises.

I personally see Nintendo's "main series" as Mario, Pokémon and Zelda. Spinoffs and crossovers not quite counted, but of course Mario Kart and Smash Bros. are huge as well. It's not really something you can define, though, because everyone has their own opinions of it.