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: Pressure-sensitive button commands for your attacks. You can change the sensitivity, but in the heat of battle, it takes quite a bit of practice to get down just how hard you need to press to initiate a certain combo.
Enemies get powered up based on how much experience the main characters spend on skills. Only the character you use gets experience. The issue is that, the way it is calculated means that if you try to use each character equally, the enemies quickly become a higher rank than all your characters. The only two really viable strategies are to only use one character, since the amount of experience used to power up one character completely doesn't raise the rank that much. The other approach is to spend almost no experience, outside the bare minimum to avoid raising the rank of the enemies at all. In both cases you power up the other characters by using them for the easy fights and not spending experience on them until you can max out all three characters. In addition, the rank of the unlocked characters is the enemy rank when you face them. So, until you max out all of the main characters and beat the game multiple times (since you can't unlock every character in one playthrough), including getting the Guide Dang It characters, your unlocked characters will always be inferior to at least one of the main characters (unless you use the aforementioned level everyone evenly approach and somehow manage to beat most of the enemies). The character ranks and main character skill purchases always apply in multiplayer, which leads to the highest upgraded character being the best choice. By the way, this is a simplification of this mechanic.
Waggle: Due to the game's use of pressure-sensitive buttons, it ended up requiring an unnecessary amount of finesse with how hard you press buttons to execute many of the game's combos, and ultimately detracted from the game's overall experience. Ironically, it's almost at its worst when attempting to use a standard PlayStation 2 controller.