Theatrhythm Curtain Call (TCC) has all the songs from the original theatrhythm. It seems to me, though, that they changed around the songs a bit, as in the notes in stuff, so it isn't just a lazy copy paste, which is nice.
I'm guessing due to the sheer amount of content, data is saved on your SD card and not the cartridge, requiring you to use the same SD Card 3ds set if you want to continue from where you left off.
Squeenix removed Series mode, which had you go throuhg five songs of one game, an opening, a field, a battle, an event, and a closing, which makes me a bit sad. However they have a lot of songs from many FF games so I'm not complaining. Also, you don't have to unlock Ultimate difficulty songs, which is nice for me.
You level up your characters and stuff. This isn't changed. However there are two stats added, Spirit and Stamina, which decrease the damage you get during Event and Field stages... I think. This time around, characters can have 4 skills of any kind (there are Reactive and Passive), instead of, say, two reactive and only one passive, which is nice. Also, you can use the Collectacard Crystarium to buff characters up however you possibly can (you still get to see the cards in your encyclopedia).
Rhythmia, Rhythm points which you get by playing songs, tend to give stuff a lot more often. Also, at the begining you're forced to unlock the ability to do anything beyond "play songs," so eh.
The characters coming over have some abilities added/removed. Example, originally Cecil had access to black magic, (fire spells and stuff), but seems to have lost them in return for some more buff abilities. This leads to some humorous things like Locke starting with an ability which adds to his luck but, at starting level, drains him to 1 hp (normally it just removes 500 hp).
Dark Notes, which had you go through a Field Stage and a Battle stage to get prizes and stuff, were replaced by Quest Maps, which are the same, but longer, and have branching paths and stuff, and possibly multiple bosses. It was "like an RPG."
There is a new type of field stage, the Airship stage. It uses the 3d capability of the 3ds to make notes come from a different perspective, it's cool.
Summons during battle have been changed a bit. Each character has a summon they tend to use, putting that character as leader tends to call their summon (example, Zack has Odin, putting him as leader will make Odin come out instead of the others). Also, there are two new summons: Knights of the Round from FFVII (which tends to kill whatever they encounter. as far as I can tell only Cloud has KoTR), and Chocobo (which... doesn't. Sometimes appears instead of whatever summon you'd usually want).
Before, you were usually capped at 7,999,999 points, forcing you to take off all abilities from your characters to obtain a 2,000,000 point stoic bonus if you want that 9,999,999 point record. Now, though, you don't have too, which removes all artificial limits from a high score.
Recruiting characters has been changed. Originally, you started with (the main) characters from Final Fantasy 1 to 13 (or Shantotto for 11, and Vaan, who is apparently the protagonist of 12, and not Balthier
), and had to collect 8 crystal shards to recruit one person, usually collected by going through Dark Notes. This time around, you start with only four characters of your choice of either 14 or 24 (depending on if you had the demo or not), but characters are easier to recruit, as they, from what I've seen, only require 4 or 6 crystal shards, and you can choose from a group of 6 of who to get. Also, getting to certain Rhythmia thresholds, you get enough crystals to get one character. Also also, Quest map bosses give several shards, which is sweet.
Versus mode is cool. You play against either an AI or another dude in a song and try to get the most points. You can inflict attacks, exbursts, on each other after you get a certain amount of Great or Critical notes. On Expert, it seems like a fair challenge, but on Ultimate it's fucking crazy. Also, some of the attacks are messed up, imo. Monster buff, for example, temporarily makes enemies harder to kill, thus making your EXburst meter not fill up as fast (you get EXburst fillage by either hitting notes for Great or Critical, or killing enemies). That isn't too bad, it's only delaying the inevitable. It also makes arrow notes spin. On Ultimate this is shite. Also, Judgment. It makes only Critical notes count towards your score, turns everything bellow that into Bad, and
drains your score for every Bad you get. Yeah, I hate this power. Versus is cool, but I just hate those two skills, the others are just nuisances at most. Play Ultimate/no exbursts if you don't want to deal with shit like this.
The game just seems to go through announcements faster than the original. I remember that seeing my dudes get exp and stuff used to take a while, but now it's rather quick.
So yeah, theatrhythm. It's cool. Really cool. Lots of stuff to do. And stuff.
Look at that Strength.