Well... as some users here have already mentioned, basically everything but in my opinion the most important thing is that the map follows the rhythm and it's not too repetitive. Flow is a quite important aspect too. Also, I think that maps should never be insanely fast if the song isn't and the other way around. I don't really care about the pp part.
There are multiple factors that are equally important.
For one, the difficulty has to reflect the song well. Having 1 minute long anime openings with 6*+ is pure insanity. I'm saying this especially in consideration of how the maps that are currently being ranked changed over the last 4 years.
The map has to have decent hitsounding. 30% sound volume throughout the entire song is unacceptable. As a common rule (with exceptions for some songs, e.g very calm ones) every map should have 100% sound volume as its peak-volume during its 'loudest' part.
The map has to have a decent flow throughout the entire song. Mistakes can happen but those should be eliminated in the ranking process. If two patterns don't go together very well (for instance you have stream going in a straight line and then you have another stream at the other end of the map going either in the same or in the opposite direction) they should be changed.
The map should have a healthy difficulty progression/curve. If you remove the last pattern of a 6.5* map and suddenly have a 4.5* map that's a sign of really sloppy mapping. Big jumps are nice and all but if the map could be SS'd by a 100k player until the end and then suddenly has 6.5* jumps in it that's just unbalanced and not enjoyable. Leading me right to the last point...
bad mapping in a good song makes for a bad map good mapping in a shit song is makes for an uninteresting map bad mapping in a bad song makes you look like a tard good mapping in a good song makes for a good map
as long as we have circles to click, no anger shall harm us