These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Some folks stick exclusively to one style of character. This naturally has led to tension between folks who subscribe to different play styles.
And then you get folks that only play certain tracks. Still Alive and Dragonforce's Through The Fire And Flames are just about permanently wedged in place on the Most Popular Tracks listing. "Still Alive" has been in the top 10 ever since Audiosurf's release and doesn't show any signs of disappearing off the list any time soon.
To be fair, "Still Alive" is included with the game, and TTFAF has a stigma as THE song to play if you want hard (right behind Silent Death).
Crowning Music of Awesome: Basically goes without saying since it's whatever music you want to play. The trope page on this very wiki also has a good list of songs to play.
Both sides of the Mono vs. Other Characters debate. Non-Monoists cite Mono players as talentless hacks that can't play a simple match-3 game and use the relative simplicity of the Normal and Pro Mono characters to dominate scoreboards. The other side of the debate is that the Monoists can't stand to play a style that doesn't have a failure condition (Hit a gray block. Goodbye high score.), and they point out the damn near impossibility of a Ninja Mono run making it to the scoreboard in contrast with Pointman Elite and Double-Vision Elite.
Every time one mentions Mono's scores not measuring up to other modes, the first reply is always " Because Mono is easy-mode".
Now that the Oct. 1 update's buffed pretty much everyone on the Pro tier but Pointman and Mono, Mono's scores are even more laughable in comparison to others. This fact may or may not be making this trope worse.
Every now and then, you'll find a file that when loaded up in the game generates a track which is considerably harder than you expect.
Special consideration goes to Silent Death. It's 10 minutes of complete silence. The track is 10 minutes of straight downhill speed.
Another good one is "Son of Flynn", a relatively quiet track from Daft Punk's score to TRON: Legacy. Traffic level is an astounding 360 on Ninja Mono. That means 360 blocks per minute or six blocks per second!!!! The far louder "Derezzed" is comparatively tame at 217 (though even that's still pretty intense, to be honest).
"Orachestral Intro" off the Gorillaz album Plastic Beach has got to be one of the calmest tracks on the album, right? Audiosurf seems to think it's about a minute of red blacks whipping in your face.
Also, any song with loud applause tends to make the track go crazy.
Occasionally, slow, mournful music—particularly sans percussion—will make Audiosurf go mad and think that it's a fast, high-speed track, downhill, tunnels, and everything. Cases in point: Randy Edelman's version of Dixie, from the Gettysburg soundtrack, and Greg Scott's performance of "Ashokan Farewell", are both much, much harder than they would appear.
Sometimes it can be inverted, when a file has a track that has (much) less intensity/difficulty than you would expect. A good example is Klonoa 2 - Polonte Ver. 2.