Managing to complete the game with the maximum number of survivors, and thus, getting the bestending for each respective character. Due to some annoying lemming-like mentality of the survivors, random falling objects, and struggling to memorize your way around the map, it's extremely difficult to do so, but the endings make the effort so worth it. It gets even better if you manage to save couples, or in one instance, an entire family along the way.
Arguably the most touching ending is Jeffrey's. Elderly couples almost always end up dead or widowed in disaster stories, and to see both Jeffrey and Adela make it out, and enjoy their remaining years together, is pure heartwarming.