I think it's common knowledge that a lot of fans hated the absence of their favorite characters and their replacement with less interesting characters. It was unsuccessful in that sense. But as far as combat goes, I think SCV is top notch.
I think it wasn't only that- some of the new mechanics introduced were more technically complicated than what fans of the series wanted. Just Impact was something I heard a lot of players complain about as an execution barrier in much the same way SF fans complain about 1f links (and I agree in both cases)
The whole game smelled like Daishi trying to shove his 3S fetish down the throats of SC fans, and 3S is the exact opposite of what SC fans want in a fighting game.
As for Garou, I think the reason Garou worked was
- the new chars were really good designs
- plenty of legacy characters
- Garou's gameplay was radically different than previous installments (and more fun- same reason Tekken 3 worked)
- many of the favorite chars were in KOF
- Rock was fujoshi-bait
Tbh it seems that USF4 is the second worst version of the game (AE is first). So much strange decisions.
The big issue with Ultra is that most of the cast is lol, but not all the cast. Dee Jay, Dhalsim, and Honda in particular are too honest now- they need stupid bullshit themselves to counter everyone else's stupid BS, or they need more damage so that damage itself is their BS.