Hm, quite general question. I hope I can come up with some helpful answers nevertheless.
What I like:
- Exploration, which requires areas that are worth looking at, things to discover; that doesn't mean I enjoy modules that force you to explore because they hide crucial stuff but it's nice to be rewarded for having a closer look around. And not necessarily in terms of treasure or something, just beautiful scenery, clever use of placeables, jokes, one-liners etc. which brings me to the next point, closely related:
- Attention to detail. I don't blame any builder if NPCs, important objects or monsters don't have their own descriptions (I reckon most players don't even care about examining them) or if the portraits or voicesets aren't fitting, if there are only standard items and clothes and default books etc. But if discover a builder actually *did* pay attention to any of these things, I'm already sold on their module.
- A good story and/or unique setting, obviously. Humor, originality, creativity. Anything I haven't seen before (unless it's anything horribly distasteful or misanthropic
'> ).
- Custom content! (If it's of high quality and used in a way that benefits the mod, of course; but generally I'm very fond of haks and custom music.)
What I don't like:
- Large areas with nothing much in it. I prefer small but exciting.
- Too much loot. I admit if there's a usable container, I'll try to nick its contents and I'll pick up everything a creature drops, no matter how useless it is. I know, it's compulsive behavior and I can't really blame that on the mod author but my enjoyment is often greater when I'm not constantly reminded of how greedy and obsessive I am.
'> So personally I prefer less but more useful loot (or automatical gold instead of junk to sell).
- Grinding. I like some challenging combats but often my interest is mostly kept by the story or the curiosity about discovering new things. I don't like hack and slash if it adds up to fighting the same type of critters over and over again. If there's some diversity in the combat, different kinds of foes or at least different looks, the occasional one-liner or conversation, good treasure, opportunities for alternative tactics etc. I may even bear with heavy hack and slash content though.
- Walls of text - which doesn't mean I don't like wordy modules, just don't give it to me all at once.
- Bugs. obviously. Even or especially the small ones that are easily corrected, like typos or missing links in conversation trees.