As an experienced player myself I look for big levels mostly, and difficult, frequent and complex patrols so I'm always cautious when I play. I dislike keyhunts (especially if the keys are very well hidden) and overly long readables (keep them short/to the point, I gave up on Finals at the Academy for this very reason) but I like hard-to-find loot, difficult jumps and looking for hidden areas. I especially like finding my way through a level by myself, take a path and see where it will take me. Most inexperienced players prefer rather linear/simple levels first to practice their skills and discover the game more in detail, and will then go onto more non-linear/complicated stuff when they're more confident. Concerning loot, when I make a mission I usually place a certain amount of loot that the players will, 99% of the time, find. This amount is usually the required amount of loot for Normal, meaning that the players can just take the shortest route and they will fill their pockets with enough loot to end the mission, without having to discover the rest. The rest of the loot is usually either placed in areas that are more difficult to access, or hidden in areas where loot is easy to find. Like if you think you cleared a room because you took these two candlesticks, but you missed this gold coinstack on the top of the bookshelf. And then I usually put 150 or 300 loot that's very well hidden, for completionist taffers.