In regards to easier difficulties, following strong and key musical points is important. It doesn't matter if the rhythm is in 1/3 or 3/4, represent it correctly. Of course it will prove a challenge to the player, but that's just the nature of the song. Don't flat out ignore a prominent vocal 3/4 if you were consistent up until it appeared, because it will very much confuse people. Breaking consistency to support simple patterning actually backfires in some (if not, all) cases. You need to think about how the player will interpret the song. The dominant layer in the music is the thing you need to take note of. It may prove a problem if the song has multiple layers that lattice back and forth. It takes true skill from a mapper to be able to properly represent this through his/her mapping: to these players, sub-layers or other miscellaneous background sounds will usually go unnoticed. Referring back to Aqo's post and his concern with the Sweet Rain osu!mania map, the synth in the background catches the player off-guard because it's not as prominent as the vocals are in that section. That is a case of how choosing a different instrument to represent the song is a poor decision. Alternatively, vocals would've been a better choice. Sticking to the dominant sounds in a selection of music is actually much easier, no matter the presented rhythm, if used correctly, consistently and with conviction. Take rock/metal music for example. Many of the vocals start on red ticks (or offbeats) before downbeats. Sliders that pass through these have a tendency to prioritize strong vocal accents as opposed to drum beats (dully noting that drum beats are sometimes weak on these downbeats, so this option is better).
I have to agree with both TheVileOne and D33d on their contributions to this discussion. For the former, he had mentioned the clarity of this declaration. We need a better way of instating this rule/guideline (honestly this can't be turned into a rule; I agree with previous arguments) so that users can have some ability and say in modding other user's maps. Leaving the opinions in the hands of the XATs will add more stress to the seemingly overfilled load of their work. Give users something to follow so that they can help enforce these rules, too. This is sort of a reminder of how there's always this struggle between user/user modding since some users add value to XAT mods or undermine the modding abilities of another because they lack a title. They refuse to listen, and then make the grave mistake of actually passing over a potentially good mod. Users have the same right and reason to mod and be able to point out things, just XATs have more authority in enforcing their own judgment, etc etc but that's really far off-topic.
With what D33d has been saying, maps need to fit the song. To create a masterpiece, a map needs to embody both: a map that respects the music and one that, through aesthetics, captures the idea of what the song is intending. The musical part of mapping is purely technical, while aesthetics is purely inspirational. You can't be on one side of the spectrum to create a truly recognizable map, especially with a community so polarized. The only people who would enjoy your maps are those on the same side. What musically inclined people in this discussion fail to see is that sometimes following the strict rhythm of a song can make a map more confusing than it needs to be. Constantly changing rhythms isn't totally enjoyable unless the first layer of a song is suggesting it. This goes back to lolcubes' variance argument and someone else's (I think a few people mentioned this but I can't pinpoint who brought this up) 'mapping to all instruments at one given time' argument. If a map's drum beat only constitutes of a consistent 1/2 rhythm, how fun would that be? Of course this is an extreme example, but my point is it lacks variety. Dynamics are completely lost and the impression of the map falls apart. Sometimes you need to take a step back and think about how to best represent the song. A map that represents every single instrument all at once ends up as a giant clusterfuck of confusion. Everything being equal in terms of which is stronger in sound is disregarded and makes the map messy. Now, what aesthetically inclined people in this discussion fail to see is that creativity can be expanded upon without sacrificing all of its properties in order to keep the map playable. It's not wrong to be creative in your ways; that's what sets apart one mapper from another. There are things that these people need to realize, though. A map made for its sheer art lacks the musical qualities that make the map for the song. As many people have been saying, you might as well "map without an mp3". It's harsh, but it's true. While art cannot merely be defined because its context varies by person, it has some limitations, that of which is gameplay. Mappers are free to create what they wish, but they are constrained the boundaries of what the song is allowing. Be reasonable with what you are creating. If your aesthetic creations do not embody the rhythm which is given by the song, then the art represents nothing. Adding rhythms that compliment the song in its own way is a form of art some people choose to use. As Sync had mentioned, good mapping won't feel like overmapping. If it goes unnoticed (as backed up by RLC and Nyquill), then there's obviously nothing wrong with it and is just a gimmick that helps convey the impression of the map from the mapper to player better. I may be overestimating the understanding and reasoning of the majority of the community around the seemingly stigmatized "overmapping" debate, however if used correctly, it can actually bring out the best in a song.
In the end, there needs to be a balance of both. Gameplay takes the absolute highest of priority because it's a combination of both divided aspects. Art and music can be one, it's just many at a time fail to accept one and blindly side with the other. Likewise, it is possible to create maps that cater to both parties: a map that clearly adheres to the music's set rhythm with appropriate settings and use of notes/sliders while exhibiting a certain feel or impression. Both are tools that must be used to make a map enjoyable, no? This can be done with no overmapping, or with a small addition that adds to the dynamic of the song. People are afraid of losing their ability to map freely and having their creativity limited, thinking that differences in a map will become less and less apparent. There's so many ways to make yourself stand out as a mapper, and it's through how you represent the combination of both. If people understand their own disposition and the situation more, it's not hard to see that it is possible to have both hand in hand.
So why can't we have both? Both sides of the spectrum just need to be willing to sacrifice a bit of their pride in order to accommodate the other. Musicality can be sacrificed to add dynamic and variance, while aesthetics can be sacrificed for playability and comfort. A map that incorporates both is definitely commendable.
Also just a clear up for some people since I see some misunderstandings, a lot of non-native speakers (namely, those from the Asian regions) use the term "funny" when they mean "fun".