Good at the beginning early years when Joss and co had a genuine fascination with the idea of redemption. So much so they did an entire spin-off show exploring it.
But after a time it came very tired, lazily written, repetitive ('close ally "goes evil" and we wonder if they can be brought back tot he side of good/ever be redeemed') and, frankly, not so much a character arc as 'this is something this character can ponder for an episode' or whatever.
Like, it was actually a character blip. A character oops. A character 'yeah I know I killed some people but I feel really bad about it so can we just move on?' No arc to be seen.
I mean, nobody in Buffy S7 main cast actually cares about redeeming themselves for past mistakes/body counts, they're just there to wrap up personal storylines or whatever.