And (2) I don't get why, as the show progresses, Angel and Angelus start to be seen as entirely different entities. On BtVS S2 that's not the case - he's the same creature, just with or without a soul. They don't consistently call him "Angel" when he's good and "Angelus" when he's bad. It makes a lot more sense than later treatments, like S4, where it's almost like a Ben/Glory arrangement. "Orpheus" is an awesome episode, but having Angelus talk about 'him' doesn't really make sense from the perspective of the earlier episodes - and it means that in S4 Angel can just get re-ensouled and be like, 'right then. I'm back; let's get back to business'. In Buffy S3, there's no doubt that Angel is the entity that killed Jenny and tortured Giles, just with a soul. And that brings a dimension to the character that by AtS S4 has just disappeared.
I totally agree with you on that point, I liked the part where they call him separate names, but thats it, I don't like the fact that they're 2 separate creatures, it was supposed to be the same person, but a demon replaces the soul, thats how vampires are treated in the Buffyverse, when a vampire is sired, the demon takes over its soul, & in Angel's case, the gypsis restored his human soul, so both the demon & the human soul are in his body, which makes him a vampire with a soul. soulless vampires feel no remorse, no love (love is an inconsistent argument in the Buffyverse), and because he can't love, he kills whoever made him feel like human, & feels pleasure torturing people.
come to think of it, the love part in vampires is a huge plot hole in the Buffyverse, Angel says he wasn't capable of love because he had no soul. Spike proved otherwise, & so did James (S3 pilot), & Darla says she loves Angel in the ep Angel in Buffy S1. my theory on Spike is that he lost his touch with his demon side for a long time (no killing), so his human side began to surface, or Angel's theory, Spike did all this to get into her pants.
anyway, I did like his dark side, it shows how strong he can get if he doesn't fight his demon while fighting the other demons, I don't think Buffy was able to kill 12 demons & set 2 vampires on fire by herself, even though she was the slayer & supposedly stronger than Angel. though we only saw Angel this strong once.
& I'd like to see Angelus more than watching Angel brood & apologize to his friends over & over in the next few episodes. Angelus in S4 was too late & unnecessary, I loved that arc, I can classify it as one of my favorite. but that doesn't mean that it made sense.