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.
Best Boss Ever: The boss from the fourth mission of the second game is a giant, apish, speaker-handed robot piloted by a mad scientist, and you have to use the power of Space Michael Jackson (voiced by Michael Jackson) to defeat him.
It's Short, so It Sucks : Some complaints...at least until you realize this is actually quite hard! Not to mention, some magazines mentioned that you could beat both games in one afternoon...but didn't complain about the length.
Part one had some of this considering you can literally play the game for an hour and beat it. However, there is an extra stage that's even harder.
Memetic Mutation: Ulala has sometimes been remixed into challening other characters to dance battles.
A very slight case. The rhythm is slightly "off" in the PS2 version of the game, especially compared to the original Dreamcast game. A skilled player can adjust to it, but it is definitely noticeable enough to cause problems and has been commented on by a number of players.
Then, there is the Game Boy Advance version.
Don't forget the PC version of Part 2, the timing is horribly inconsistent and sometimes the game would go out of sync, usually after minimizing it, but sometimes for no reason at all! The Japanese dub can crash the game(especially on report 4), not to mention small stuff like it being a 2011 release with no 1080p option without hacking, and the volume meters being inexplicably stuck inside the game's setup launcher, which not only plays an incredibly loud song every time you open it, but you might have to fiddle with registry entries just to get it to save!
The PC port has been fixed as of September 16th, 2014. Syncing and crashing issues are gone, the game now supports 1080p, FXAA, and gamepad prompts by default, and the config launcher no longer plays any music. Audio seems to have also been tweaked somewhat. The Japanese dub is no longer available though.
That One Boss: Evila, Giant Evila and Purge the King have made many people toss their controllers.
The latter two because you have to quite literally do the opposite of what they tell you to do. And when you're so used to doing exactly what they say...you can see why people recommend holding the controller upside down. Purge the King also only gives you three chances to screw up!
Blank TV can also be irritating at times, seeing as he has no exact rhythm. Also, if you screw up, he makes it EVEN HARDER. And you don't have many hearts to screw up with this boss.
The first part of the second level in Part one. You have to rescue the space captain and the other staff members; which gets pretty hard when they send some fast commands at you. (Players recommend that, unless your thumb goes fast enough across the D-Pad, you use your two fingers)
For that matter, any level where you have to either get delayed commands ("Up.....up hey!") or where they send a ton of commands at you. (There is one part in stage 4 in Part 2 where you have twenty two commands to repeat!)
Woolseyism: Ulala's name is a localization of Urara (See Meaningful Name), which is a common Japanese name. However, the pronounciation turns it into a pun, since they prounce it as "Ooh-la-la"...which is a phrase that is often uttered by people when they see beautiful women. Conveniently this is part of the game. Fridge Brilliance perhaps?