There's a Metal Gear wiki out there but IIRC, there are spoilers for MGS4 in the summaries for games like MGS3, so that's probably not the way to go I'd suggest playing MGS1-3 first if you want to enjoy the story in full. That might seem unreasonable but they're some of the best games ever, I really don't think you'll be disappointed. That said, I think you'll still enjoy MGS4 even without the relevant backstory. Anyway, if you want to try the wiki, start here and then scroll down and click on the next event in the "event chronology" (in this case, "Operation Snake Eater") and keep doing so, but stop before you get to "Liquid Sun." The only major spoiler I remember is the identity of Snake's mother, so you should get by alright with it. I hope they haven't changed it since then.