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.
Beethoven Virus which as the title says is inspirited by Beethoven's "Pathetique".
Best Boss Ever: There are some memorable boss style charts in World Max. Try playing the full version of Deja Vu where the chart can randomly change at two points.
The speed of NXA's boss song Final Audition 2-X hits seventeen steps per second in places. God only knows what Fiesta has in store... Vacuum Cleaner in Fiesta EX!
Complacent Gaming Syndrome: Many of the Mexican speed players love to play the hardest songs over and over. This backfired spectacularly during the World Pump Festival a few years ago, when the random songs chosen for the first two rounds were two of the easiest ones, and none of the Mexican players made it past the 2nd round due to lack of practice on said songs.
Ear Worm: Kara's Wanna from Fiesta. It is so much an Ear Worm that there is a dedicated course for just that song, five times in a row. The course is called Wanna's Train.
That One Boss: And how! Every mix since Exceed seems to have at least one.
Dignity on Exceed
Canon-D and Solitary 2 on Exceed 2
Love Is A Danger Zone 2 on Zero
Chimera and Final Audition Episode 2-2 on NX
Final Audition Episode 2-X on NXA
Sorceress Elise and Vacuum on Fiesta
Cleaner and Crashday on Fiesta EX
Flew Far Faster and Ignis Fatuus on Fiesta 2
Even the Pro series gets involved as well: VVV (not VVVVVV), Rockhill, and Dream to Nightmare are just a few of the very difficult charts.
They Changed It, Now It Sucks: Pump It Up Pro uses the StepMania engine instead of Andamiro's engine. While most of the basic features are in, including counting combos on holds (however, it doesn't do it the same way the main series does however, by counting every 8th note instead of using arbitrary "tickcounts"), one thing missing is Split BPM, or the ability to have two simultaneously playing charts for the same song have different BPM changes and stops. An example can be found with Phantom Hard and Crazy.
The current main series, PIU Fiesta, changes many things related to how to select songs and options. The core gameplay is still the same, however.
The recent fork-turned-official StepMania 5 (Pro 2 was based off what was then StepMania 4) finally adds support for split BPM's in its extended ".ssc" file format. Yay.