You want in-depth guides? Well there aren't any...
I will post here all the useful things I've found:
[Basic]
[*](Incomplete) Beginner's terminology guide
t/482554Read this first to get it out of the way.
[*]Wiki
https://osu.ppy.sh/wiki/Main_PageRead all the pages in the
Beatmap Editor and the
Online Editing and Ranking sections. You should know pretty much everything in here by now, but just in case there are any gaps...
[*]The Editor itself
Just click every button and menu item to see what they do =w=
[Intermediate]
[*]Music Theory
t/58959This tells you how emphasis is USUALLY done in "normal" songs. However, the emphasis will always depend on the song itself! So after reading this, try to listen for which beats are more important than others in actual songs.
[*]Charles' Mapping Theory
https://osu.ppy.sh/u/85000Goes into why certain patterns PLAY well. Not useful in itself, but very useful to keep in mind when analysing beatmaps.
[*]A trivial bit on aesthetics
t/465718This tries to explore aesthetics and visuals a bit more. The gem of this post is in the discussion, definitely read this to the end!
[*]-Mo-'s Mapping Theory
t/479828Personally don't agree with this, but it's good to keep these points in mind when analysing beatmaps.
[*]General
t/435458This goes more into how to improve and practice mapping, less about any specifics.
[*]Raika's hitsound guide
https://osu.ppy.sh/s/224758This one is a beatmap. Open this up in the editor to follow the tutorial
[*]Guide Compendium
t/441929Actually mostly useless. But it contains a lot of links! Read them all because why not. This actually contains most of what I've posted above, but I think the ones above are the more important ones.
[Advanced]
Woops, sorry, there's nothing... Map more xP
But if you're here, re-read the first few guides I linked, maybe.
Edit: wtf formatting is fucking broken.