Doing this is Anti-Consumerist, the best thing for Microsoft is to invest in creating their own 1st party studios or invest in talented independent studios, get more quality developers that are fresh to the industry and create their own franchises from scratch.

This is what Sony has done, it's what Nintendo did from the beginning, same goes for Sega (even though they eventually failed as a platform holder, but their franchises are still well known).

Buying everything is seen as stealing by the majority of the community and it basically destroys any kind of positive image you may be trying to create. Now if you happen to be the market leader it's not so bad, because you already have the system where most people go to buy their games, so these kinds of actions don't have the same kind of negative effect to them that they do for the under dog.

Anyway best thing is to forget the multiplatform titles and look out for interesting new IPs, from new developers that don't already have a huge reputation, buying those franchises insures you get variety, create your own identity and your supporting the growth of the industry, rather than tainting the few gems of the industry.

It just released on Vita.  Are you high?

MS had all last generation to this, but instead they continued to demonstrate that they will never commit to console gaming for the long haul.

That's great, but did you bother to read the OP? Or just the title even? The OP is not asking about which game could save a console, but rather what one franchise can put Microsoft in first place in the console war.

Maybe GTA + COD would put them in first place.

I think Halo didn't say the first xb

I know this may sound crazy, but I think the best combo is Madden and Fifa. That will grab the American / European market fast.

Actually it did, it outsold the Gamecube and making xbox at least somewhat relevant. Just like how it contribute in Xbox one outseling the Wii U despite the Wii U being cheaper and having a year head start. Halo did a lot. I wonder what a Minecraft sequal will do.

GTA would help but I don't know if that would get them #1 in WW sales. GTA+COD probably would though.

Purchasing a franchise would be a bad move. MS has repaired their image quite a bit, but they are still under scrutiny. Purchasing anything of size would cause a *lot* of backdraft that could damage them and the franchise purchased. However, all things being equal, diversification is what they need. So I would actually say The Elder Scrolls. It's a franchise still growing and different from their current lineup. However, as I said, purchase is unwise. Now, investing in creating their *own* franchise of similar style/size/scope/genre/etc would be a wise move.