@rigas: peace walker was 2010, mgs4 was 2008, why would they go out of order now?
A ton of people make the mistake in thinking Peace Walker came between 3 and 4. I think it's either them just remembering there was a PSP Metal Gear that came out between 3 and 4, or because it's bundled with 2 and 3 in the HD Collection.
yeah portable ops seems like the forgotten one of the series. i'm not sure if it's rightfully so because i've never had a psp or vita, but i always just lumped peace walker in with it myself as "things i'll probably never play, but happened, and are probably somewhat important".