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.
Scrappy Mechanic: The voice-based tests in both games. It can be very hard for the system to pick up certain words, leading to skewed Brain Ages (and sometimes the game even totally aborts the test if it can't hear you properly). Thankfully, there's an option (meant for use in loud environments) to not allow these tests to show up during Brain Age testing.
Similarly, any of the minigames that forces you to write under pressure (for example, Word Attack: Space). Brain Age's inability to correctly identify letters becomes extremely frustrating when you're unable to zap that "e"-shaped bullet before it destroys your ship because the game insists what you're writing is an "f."
Stop Helping Me!: Dr. Kawashima's advice can come off as incredibly condescending, given time.
Dr. Kawashima (said with a disappointed face): “Hmm, a little tired, are we?”