So I've never played the Metro series, but they've always intrigued me. I've played quiet a bit of Stalker in the it's various incarnations. For SoC finishing the Agroprom Undeground (the part you just finished), gets you into the game proper. By now you have an idea how the game works, you've finally got a decent gun or two (you did snag a good AK-74 right?), and from there things open up a lot. The quests are still the fetch and carry, find and kill, or find and talk to (but let's be honest aren't all quests usually a variation on that?). You'll start to get a lot more of the game's backstory too, as you start to get right in the middle of everything.
-Jenrick