Me too!

leo you do walk into these things....had you said 360 version i would have been sceptical, but PS3 version probably won't get half what SSBB gets.

I would say it sells near 14 Million like the last 2 did.

 If by 2 biggest you mean:

1) Physically biggest, as in bulkiest

or

2) Biggest as in #2 and #3 out of 3 consoles

Yes, they're the biggest. 

GTA4, however, will sell like crazy. My guess is

Opening week

360: 1.5-2 million

PS3: 1 million

Lifetime

360:  13 million

PS3: 8 million

I think it'll sell more PS3 systems than 360, though, since most of the 360 adopters probably hopped on between Bioshock and this coming Christmas, Halo 3 being the flagship title right in the middle of that span.  

Being that the PS3 and XBox 360 combined have barely sold over 20 Million units I can't see this game breaking 10 Million units across both platforms ...

Im guessing lifetime sales of 13.5M in total. 9M for 360 4.5M for PS3.

GTA4 vs Halo 3

Halo 3 ltd: 7m
GTA4 (360): 13m
GTA4 (PS3): 6m

lol, so much is wrong with the start of this thread. Seriously, I challenge somebody to find something that's right in what leo-j said.

20 million? No way. The entire Metal Gear, Mortal Kombat, Halo and Castlevania franchises have sold 20 million. I expect by the end of this generation for PS3 and 360 sales combined to equal 100 million at most, and I think that's being generous TBH. Even if there were 100 million ps3s +360s by 2011/12, you're asking for a 20% attach rate.

If you really believe your own hype, you're going to be heartbroken.

GTA is a huge series, but it sold well becuase it had the userbase that could support it. Ya know 100 million on PS2. While when it went on Xbox only about 2 million. So it's looking like a 1/10 of userbase kinda thing on both.

So now it's going to deal with much less than it normally would have which makes me wonder if it could hit those numbers. Maybe if it was released on PS2 and Wii as well, 20 million would very very possible all combined. But I don't know if PS3 and 360 will have the userbase to support those kinda sales.

Not to mention it sold beastly on the PS2 cause it was a dominant exclusive which gives extra sales and then alright on the Xbox becuase it finally got it. The same kinda marketing ain't behind it cause its multiplatform. It'll sell a lot of brandname of course but I just don't know about 20 million. Its possible but not probable but right now if the same userbase increase for PS3 and 360 continue. I think both would need a userbase of 50 million to have that even be close to possible.

1. biggest game of the century-we are only 7 years into this century. Biggest game this century so far, you can argue that.

2. 20 million seems a bit high, but it could eventually get there. it should reach 15+ million for sure though.

3.GTA4 will probably sell best on the 360 especially with the exclusive content.