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.
A game I'm developing with some friends:
www.xnagg.com/zombieasteroids/publish.htm
It is largely a technical exercise but feedback is appreciated.