A true PS2 classic, although try getting hold of MGS2:Substance for the full experience..
The graphics are still outstanding for the PS2 or any console, even 4 years on from when it was released. This hits you as soon as the game starts with Snake aboard the tanker. The rain effect is truly amazing, splashing puddles, rain hitting Snake and reflections on the wet deck add to the feeling of being on a ship in a storm.
I didn't find the sound mind-blowing, but it does the job well. The sounds of the rain and thunder on the tanker level was the best bit for me.
With Sons of Liberty you only get a few extras. You can take on the Bosses again one by one. There's also a Demo theatre where you can change the cast of characters from the cut-scenes, so if you think it would be a laugh to see a load of old women running around on the tanker with guns, you can. Most soldiers have dogtags which you can take from them by holding them up with a gun. Getting more dogtags will unlock special items like Snake's Bandana giving infinate ammo for your weapons, or stealth camoflauge. Getting more dogtags will prolong replay value for a bit, but once you've played through two or three times, you will have seen it all.
MGS2:Sons of Liberty is an awesome game that no PS2 owner should miss out on. Sons of Liberty is extremely cheap and easy to get hold of, although if your willing to shell out quite a few notes on MGS2:Substance, I would recommend it. You get the full story mode and a stack load of extras you wont find on Sons of Liberty.