Like the title says, what games, or franchises becoming exclusive to a certain platform would be a big deal for you? Big deal, as in you would go out and buy a system that you would have otherwise had no intention of ever buying.

For me, I'd have to say:

Mass Effect

Deus Ex

Metal Gear Solid (used to be exclusive)

Elder Scrolls

Dragon's Dogma (call me crazy, I loved this game, and if it gets a sequel it could be massive)

Mass Effect

metal Gear

Elder Scrolls

Call of duty

Battlefield

Grand Theft Auto

I don't think we will have to worry about any of them doing that though lol  Well maybe Metal Gear.

Probably the WWE games or if TNA made games.

Well yes, but some people might be really big fans of some smaller games, that would be a bid deal for them if it went exclusive.

Like Dragons Dogma for me

Grand Theft Auto or Call of Duty

Assassin's Creed III

GTA, (though I skipped IV) and Assassin's Creed. The chances of them going exclusive are pretty slim though. CoD would be a big deal in terms of a WOW factor, though the chances of it going exclusive are just as slim as aforementioned games.

Assassin's Creed
Batman: Arkham games
Dead Space
Mass Effect

still wouldn't buy an XBOX though

I'd be a bit bummed if Mass Effect 4 went exclusive to Wii U or Nextbox, but as we've already played the definitive trilogy it would only be a little bit of a bummer.

I'd be more miffed if Dragon Age went exclusive to Wii U or Nextbox because there's unfinished business in that story.

I haven't played Dark Souls yet, but once I do I'm sure I would not like losing Dark Souls 2 to another console, but as it sells best on PS I doubt it will move away from that platform.

Mass Effect
Fifa