Epic dev lead Cliff Bleszinski has said that the narrative for Gears of War 2 will be beefed up over the original game, and pointed to the newly released teaser trailer for clues as to what to expect.
"Narrative is one of those things that is incredibly important in a video game," he said. "The teaser that we released alludes to an even more interesting narrative set-up for Gears 2."
The trailer contains the line, "If something happens to me, promise me you'll look for Maria." This may allude to some love interest, but considering Marcus is built like a bull, we doubt he's capable of the "other" physical thing, you know, than killing people. It sounds as though the voice in the trailer isn't Marcus's, anyway, so it's probably something to do with Marcus looking for someone else's wife/girlfriend/dog.
Or something. We don't know. It's Friday and we haven't slept for a week. Read the rest of that interview for ramblings about the artist formally called Prince and fire marshals "nixing" things.