CT had a kinda small roster with 12 characters and CS increased that 15 (18 with the 3 DLC chars), it may sound small compared to other fighters but every single character has a unique style. What do you prefer, quality or quantity ?
I prefer both. Quality and Quantity. Look a Street Fighter IV and Super Street Fighter IV. SF IV had 19 characters all of them felt unique also, even when you compare Ken to Ryu. SSFIV added 10 more charaters to the roster for a total of 29 (plus 4 with the upcoming Arcade Edition DLC for a total of 33). In my opinion this amount of characters adds more way replay value than 18 Characters and a Story mode.
Now, one might say that SFIV only has so many characters because its not a new franchise, that they just took characters from previous games and rendered them in 3D. But that takes as much work as creating a new character, specially when balance is so important to Capcom. Also, Arc System works could have done the same. They could have continued the Guilty Gear franchise and just add 12 new characters to that (which would have been much better) but the reason they didn't was this:
"The generation of Guilty Gear players has become a certain age – maybe a little bit too old for playing games. So making that reset brings in a new generation of fighting game players. Then they will be with us for the next few years". Toshimichi Hori - Arc Systems Works
So instead of letting a franchise evolve, they let it die and start again for the most illogical of reasons. Gamers don't stop liking games when they become a certain age. Its the reason why Street Fighter, Super Mario and Donkey Kong are still around!
Every single fighter is different, not only in style and characters but also with inputs and timing so if you are used to a certain game you have to adapt to a new one even if the inputs are the same.
I know this, mate.

I'm no stranger to 2D fighters, I've played pretty much every 2D fighter worth its salt except Killer Instinct. I can adapt to 2D fighters quite well, I'm no tournament player but I'm quite decent, I think. I've played the game for a week now, I have completed Arcade on Hell difficulty and Legion on hard, I have beaten some players with a lot more experience and it still feels a bit stiff to me and I still struggle with with pulling off moves like Carnage Scissors successfully, while I have no problem pulling off similar moves in GGX and other 2D fighters.
What I love about Blazblue is the the soundtrack which is just as awesome as I thought it would be!
I'm glad there are people out there who did enjoy playing story mode but its just not for me, When I put a fighting game in, I want the focus of the game to be fighting, I'd rather have all that artwork unlocked through other modes, like Survival and Time-attack.