i asume you mean MGS2 sons of liberty = substance, which is a crappy game, the cinematics are great (graphics) but the story is so damn lame, the game is way too short (there's only two levels, and n the last one you just get to play half the map). i was loving that game until i get to be inside arsenal gear, you don't get to unlock all the doors (unlike MGS), and then the game ends (after a nearly 1 hour finale, pretty impressive videos, but yet lame), i expected a lot more.
The gameplay is a different story, you can do nearly ANYTHING in that game, it's all up to you. your not limited to a certain comands or movements. there are lots of things that you can do, sadly you don't get to use then all.
MGS (ps1), is totally different. Is a masterpiece in everyway. excellent story, and equally great gameplay (limited to the ps1 power O/C)
i was comparing HALO to MGS1, but HALO is still a great game. They're both different, but i prefer MGS.