So yeah. Theatrhythm actually has quite some hard things to it.
I really despise the habit of putting swipe notes directly after a stream of 1/2 touch notes. The game often senses the tap of the previous note as "putting the pen down to swipe", and causes a BAD hit. Trying to swipe while your pen is still down also often causes a BAD hit.
Perfect scores for any difficulty, any combo count is 7999999. The game recognizes CRITICAL hits as 7999999 \ #comboforselecteddifficulty . I'm using a team consisting of the Onion Knight, Terra, Vaan and Lightning at the moment. The difference in use of character selection is rather negligible, from my experience. Save a few "bonus" abilities, such as lightning using Libra to determine one of a single boss's possible drops in a Chaos Shrine score.
It's fun, don't get me wrong, but character growth isn't a drive like it's purported to be in the tutorial. Have fun playing Basic charts forever until you can play harder charts, too. You start off with Series mode, consisting of Basic charts from every Final Fantasy game. Once you clear a Series's songs, you unlock them in Challenge mode, which is essentially free play.
Within Challenge Mode, you can now play the Expert Score for each unlocked song! Once you beat that with an A grade or higher, an Ultimate Score becomes available. Once you finish all songs in a series on Expert Mode, you then unlock the ability to play the harder difficulties of that series in Series Mode. Same goes for Ultimate Charts.
Chaos Shrine is where the fun is. Every chart is randomly generated from a number of "possible" blocks within each segment of the song, allowing for a bit more variety in the charts. They're generally harder than Expert but easier than Ultimate charts, from my experience. When you beat a Dark Note within the Chaos Shrine, you can get different items depending on which boss you defeated and how quickly, etc. Each dark note has 9 possible boss drops from three separate bosses. Which boss you fight is decided by how well you do in the Field Song at the start of each Dark Note.