I like them huge and deep. A massive open world with a long, epic story and open ending. Conversations, fully voiced ones like Mass Effect, but I'll tolerate the non-voiced conversations like the Fallout ones. Levels are quite nice but sometimes they just don't work, eg I hear in oblivion you can get easily killed by a rat at low levels, that's not good. Levels need to a way of upgrading skill trees and getting perks, but instead of having level 50 rats, just make it so at level 4 rats are a threat because your best weapon is a stick and as you level up, rats stay rat-strength and you get better armour and weapons and start fighting super mutants or something. Rats are still there because rats are everywhere, but they're rats, they do 0.01% damage after a while. This means enemy diversity. Rats, to small mammals, to large mammals, to people, to heavily armoured people, to crazy shit. Also, mainly in Fallout's case, I don't care if it's the first pistol in the game, a bullet to an unarmoured head will ALWAYS kill a person. ALWAYS. And never, never ever ever should the player EVER feel like their options are being restricted by the game. EVER. I like lots of everything so after hundreds of hours of playing there is still places to see, items to get, to upgrade, conversation options to pick, and enemies (or maybe allies) to kill.