I think a bunch of the cast is fun, or at least has the potential to be fun. I love Bison, because I'm constantly vying for the best positioning and being rewarded for it. Urien is fun for a different reason, obviously due to his normals and AR goofy things he can do. Guile is incredibly straightforward with his design allowing people to get to the core of the fun much quicker than other characters. Rashid is a lot more fun "now" because he can do damage and still pull off ridiculous things even without v-trigger.
On the flipside, some characters don't feel as fun. Like Balrog, which is the reason I quit playing him. He feels like he's a little too simplistic, and can bully people easier than most other characters. Like the game caters to him too well, if that makes sense. Ryu lost what was fun by making his tools harder to use - so all that positioning Daigo does and such doesn't get rewarded like it did. I guess that goes hand in hand with nerfing characters, although FANG players love the challenge (all three of them).
I don't think it's primarily about normals being stubby (well, part of it) or such, but whether or not a character works well within the confines of the game's system. Obviously this isn't for every single character, as Akuma is fun because of all the variations to his combos on whether you want stun or damage, but if you have to struggle more and get less rewards out of it, it's probably not as a enjoyable. Ken players can make him work, and he's arguably still strong, but the pay off isn't as good. Balrog is too strong, and therefore it doesn't feel that much fun playing him.
However, I think some characters just transition to different things as balance happens, but they should still consider how a character works in the game to better improve the immediacy of fun or avoid souring it.
Edit: Looking back at other games, that's probably a commonplace problem. Gundam was only fun with certain characters to me because someone them would either do shit well, or do the same shit but for worse. Why even fuck with Kapool? Seriously poor Kapool though.