MGS series.

A game that probably defined a genre of gaming, had an Oscar worthy story, great characters and even good voice acting or a generic FPS...?

I'll go with MGS.

Remembering we aren't talking about quality here. Halo has to be the winner here. Halo was the xbox. The original xbox sold largely on the strength of the halo franchise. That itself is a huge feat. But not only that, theres a reason why whenever a great fps game comes out people ask "is it a halo killer?". Its because halo is largely responsible for the popularisation of the console fps. Yes Goldeneye existed long before it but it didn't lead the fps genre into the dominance that it has today whereas halo did.

I've never played a halo but I love FPS. However I play every MGS and because of that I love the stealth genre