I'd do an ER knockoff - an understaffed Starfleet medical clinic in an underserved, urban alien setting. Maybe an Orion city or something on Bajor. Something in the ionosphere interferes with modern equipment, so the level of medical magic is much reduced, and new Federation doctors who arrive are in shock at the primitive techniques they have to employ. There would be a lot of gritty trauma scenes, but the meat and potatoes would be the relationships between the characters.