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.
The "real guitar" that it works with is awkward to use, both as a game controller and as a standalone instrument. One cannot simultaneously play the game AND use the guitar as a normal guitar, otherwise the game registers numerous over-strums.
The AirStrike drum peripheral was intended to give a quieter experience and be more space friendly than "traditional" drum controllers; however, the sensing technology was finicky at best to completely nonfunctional at worst; the player had to use the "special" drum sticks which came with the AirStrike and hold them in a specific way in order for the unit to register "hits" on the "drumheads".
While using Rock Band or Guitar Hero instruments, there are certain quirks. For guitars, the tilt sensor cannot be used to summon Mojo Power, and the whammy bar doesn't manipulate sustained notes; instead, it is used for summoning Mojo. For drums, it is difficult to summon Mojo Power without breaking combo due to the game's default drum controller using an extra pedal for this function. The player can enable automatic power summoning whenever the Mojo meter is maxed out; however, this can lead to inopportune power summonings.
The game claims to teach you guitar. It doesn't.
Downloadable content does not work, asking for a nonexistent title update.
The drum track uses a regular round note for the bass pedal in the middle of the target area instead of a special note spanning the target area, which can confuse some players, particularly those accustomed to the Guitar Hero drum kit, which uses 5 regular inputs plus the bass pedal. This is rather befuddling since the guitar track uses a target area-spanning note for open notes.