Although the weakest in the series MGS2 is still a legendary game, the original release was lacking in a few areas but that was fixed with the updated version "Substance" but the ultimate version of substance has a few more additions that makes it a must have for any MGS fan.
Just bare in mind that certain aspects of the game (like the camera and the controls) are a bit dated but it's fairly easy to get past.
Metal Gear Solid 2 is one of the few instances I can remember in videogame sagas that actually builds upon the original to create an even more superb masterpiece. It is simply breathtaking, an action/thriller/mystery work of art.
This edition in particular is recommended to all Metal Gear fans.