Great choice on picking up the MGS essential collection, Nanner. You've just taken your first step into a larger world... or something like that. I eagerly ran out and bought that thing on the day it was released. Fantastic deal, great looking set, and you can't beat having the first game in PS2 style packaging to match the others.
Sure the game takes some over the top Japanese anime-like liberties with reason and sense, but the experience of playing them is so unique and enjoyable that it is easy enough just go along with it.
If you really enjoyed the first one, and I mean really enjoyed it to the point of wanting to play it again, then you definitely want to pick up the remake for the Gamecube. Mostly the same game but with upgraded graphics and a few extra features (for example, when you get shot you will leave a trail of blood, so you have to use bandages). Oddly they redubbed the voice acting, but with almost all of the same actors, and didn't quite do as good of a job as the original IMHO. Still a pretty cool game though. I'd recommend the original for newcomers, and the remake for someone who wishes to revisit the game again later.