Interesting NPC's, Populated Roads/Cities/Ect... are a must for me in addition to what you mentioned. Animation mods, Killmove mods, Dismemberment Mods, Burn/Shock/Freeze Effects, and the like also end up getting a big priority from me. For Arrow mods, nothing beats Locational Damage since it turns those arrows you painstakingly aim at the enemies' eyeballs actually kill them in 1 shot. Its way too easy to jump from a few mods to the max. XD