Metal Gear Solid is certainly not a niche product. No game that sells in the 3-5m range is anything approaching niche status. At the same time, it also doesn't draw the huge mass market crowd that you see from games like Grand Theft Auto, Gran Turismo, Halo, Guitar Hero, etc. You could say that it's a game for "gamers", those who obsessively follow news online and purchase lots of games. For that reason, I think it's unlikely to move that many systems, because those who are the biggest Metal Gear fans are the same people who mostly already own consoles.
The reviews trickling in have been interesting for the latest Metal Gear Solid, since they seem to be either 10/10 "greatest game ever!" or 8/10 "too many cinematics/cut scenes". You can pretty much tell whether or not the reviewer was a huge Kojima fan based on the score awarded. (Every review says that this game will be loved by its current fans... and confuse the hell out of newcomers.) The fact that Metal Gear Solid 4 seems to cater to the existing fan base may also limit its sales potential somewhat, although we'll never know what it's true sales would have been, since it's going to be bundled with all those systems.
End of 2008 totals: Wii 42m, 360 24m, PS3 18.5m (made Jan. 4, 2008)
