YMMV / O2Jam

• Fan Discontinuity: Most fans of the original PC game don't acknowledge the mobile spinoffs or are even aware they exist, mainly since they are outsourced games with drastically different mechanics and the only real connection being the songlist. Instead, EZ2ON REBOOT : R, particularly after the O2Jam collaboration DLC was released for it, is seen as a more proper successor to the original O2Jam (especially since it features courses that exclusively have 7-key mode and even have the original charts).
• First Installment Wins: The original PC game is easily the most iconic installment, being one of the earliest examples of an MMO rhythm game, free-to-start thus making it affordable for those who cannot afford contemporary paid rhythm games, and not requiring any peripherals (a high-performance keyboard helps, but a conventional one works just fine). Its later iterations on mobile are largely forgotten, being seen as cheap cash-ins on the original brand. About the only thing really seen as a worthy successor to the original is EZ2ON REBOOT : R, which became viewed as a Spiritual Successor thanks to the release of the O2Jam collaboration DLC.
• Hilarious in Hindsight: The original PC game was derided by beatmania IIDX players for being a IIDX ripoff. Years later in 2010, beatmania IIDX 17 SIRIUS would implement Charge Notes that are done just like O2Jam's long notes — counted for two notes, and the initial press and the release are timed, with an automatic Poor (e.g. a missed note) for the latter if released far too early or over-held.
• Germans Love David Hasselhoff: Besides South Korea, O2Jam PC is also famous in China and Southeast Asia, especially The Philippines. They've even made private servers for it!
• Porting Disaster: The 2023 Steam release by Valofe. It's a port of the mobile game by the same team, which is already not really a popular title amongst O2Jam fans due to being seen as a cheap cash-in on the brand with the songs being the only connection to the original game, and they couldn't even get that right: songs sometimes garble up, some of the note judgements don't work, sometimes the game will just soft-lock and stay in indefinite loading after picking a song, the Fever sound effect is incredibly loud relative to the background track, some songs use incorrect artwork, and perhaps worst of all, the price of the VIP subscription was raised from 1 USD a month to thirteen...which, due to an error, is charged every single day, meaning that the subscription actually costs about 390 USD per month!! For the price of one month of O2Jam Steam VIP, you can subscribe to the mobile versions for a little over 30 years!
• Scrappy Mechanic:
  • In O2Jam PC, “hold” notes don’t just have to be pressed with perfect timing, they also have to be released with perfect timing. As time passed, more and more charts featured hold notes to increase the difficulty, leading rhythm game players to deride the practice as "noodles". Fortunately, the mobile installments fixes this by letting the players press the "hold" notes without having to release them perfectly.
  • O2Jam PC stops you from earning EXP in single-player mode beginning at level 10. Which leads to another problem...
  • For no good reason, O2Jam PC forces all players within the same lobby to use the same speed multiplier, which routinely leads to players arguing over which speed setting should be used (such as players who prefer the x5 speed setting repeatedly spamming "x5x5x5x5x5").
• Spiritual Adaptation: PC was pretty much an MMO edition of beatmania IIDX, with the use of seven white and blue alternating lanes (albeit with the center lane being yellow) and keysounded songs. It even features hold notes ages before IIDX implemented them (granted, Keyboardmania from the same franchise as IIDX did them a few years prior), implemeneted the same way (count as two notes, releasing the note is timed).
• That One Attack: SHK's "Identity" songs are infamous for the "Heok smash" pattern, in which notes form the Korean character 헉. To this date, there are no verified human attempts at comboing the entire sequence. Just in case you think the PC version being gone means this pattern is a thing of the past, this pattern makes a dastardly return in EZ2ON REBOOT : R as part of the O2Jam collaboration DLC, when playing the Brain Stretch course.
• They Changed It, Now It Sucks!: Everfree’s (one of O2Se. Team composers) In My Dream had added lyrics in U, but was instrumental in a previous version. Some Korean fans prefer the instrumental / ''PC'' version.