Excellent question. To evoke the Fallout feel, I'll be awarding xp not just for kills. Xp will be given when locations are discovered, feats are accomplished and areas investigated. With roleplaying, exploration, and some vore (I feel either being prey or predator should award some amount) will have levelling move at a fair pace. Expect early levelling to be fast, but I'll be trying to keep the pace up.