I'd like to write briefly about rhythm games.
Parappa the Rapper was the first exposure many in the west had to rhythm games. The endearing characters, the funky music, and the outright comical plot made a fascinating game people enjoyed.
In addition, for being a Japanese game, the English was done rather well -- given how this was during a time where English voicework in games were still very questionable, it was rather notable. It turns out that the game's audio was originally done in English, so that explained the quality, even if sometimes the grammar doesn't make perfect sense.
Still, one of the problems that popped up in Parappa the Rapper came when it was the player's turn. The game was set up as a call-and-response style of game, where the opponent of the stage said a line consisting of button presses, and then the player would repeat said button presses. What was not clear was when exactly the player's turn was supposed to start. In addition, the underlying mechanics of what exactly was "good" and "bad" was unclear.
The next installment of the series, although it was more of a spiritual successor, addressed the issue of when exactly do the players start their turn.
Still, it wasn't entirely clear just how to actually accomplish the best rating since strictly mimicking the opponent will just net you an acceptable rating. So in the actual sequel, Parappa the Rapper 2, they added in meters along the bottom that judge how your current line did in getting to a "cool" rating.
However, even though there was a visual display of what you're supposed to do, the rules themselves felt very inconsistent. Notice Parappa strictly mimicking and sometimes getting halfway up to Cool, but sometimes failing, despite strictly mimicking. The intention was to have the player freestyle and do their own thing, but even that doesn't exactly work all the time.
Implementing your rules in a way that makes sense and is consistent is key to player satisfaction. The fact that the freestyle doesn't work all the time, or why some freestyle is better than others isn't easily understandable even by someone who's beaten the game.
Consistency is very good. This doesn't mean you need to remove randomness of any sort, but as long as you're clear what parts are randomness and not just buggy implementation, it's absolutely fine.
Like I had wrote about earlier, you need to also manage player expectation when you're making a game. Just like a performance, everything needs to appear intentional, or else the audience will assume something was a mistake that wasn't.
And for your enjoyment, here's a player who edited the files to make one of the stages in Parappa the Rapper 2 far more interesting.