In terms of what use I'd have for fan created adventures, as a new DM I'm interested in how other DMs approach adventure writing, as opposed to the slick professional efforts of published adventures. I'd run it if it stood out to me and made me want to
play it. Otherwise it all contributes to the collective learning experience!
As far as what sort of adventures I'd look for, self contained, high-flavour, adaptable (to one's own setting), with an original use of existing material or, if it seems well done, something entirely new. Something that can be slotted in as a side/environmental/interlude quest, or modified to fit into a campaign arc. Anything too involved or with
unnecessary/poor quality fluff would be a turn off.
And there you have my 2 cents..
[EDIT] If it's a dungeon or extensively dungeon-based adventure, the map construction needs to be good. If it's more free roaming/investigative then the story needs to be good, and there needs to be enough intrigue to propel the adventure forward. Of the two I'd probably use the former to pilfer resources, and the latter either as is or steal the concept and bend it to my uses.