Create a good story. Anybody who bothers to play low-graphic RPG's will want to be sucked into the storyline or they'll quit after a little while. It's the reason why people still play old games, nostalgia is one thing, but mostly because the stories used to be pretty good.

I rarely play new shooters these days, because it's always the same thing in and out, try to mix in new things along the storyline to keep the player enthoused.