Plot hole: In the flashbacks, there is hardly any use of language from the 1940s.
Plot hole: After learning about the prophecy, the gang realise that Spike's headed off already, getting a head start. Angel grabs another car and heads after him, but why use a car? We find out in the first or second episode this series that he's got access to a helicopter, which he uses to get a long way ahead of some bad guys, and which would have saved a lot of hassle this time. Can't imagine Wolfram and Hart's pilots only work in the daytime.
Answer: Due to his epiphany, Angel basically had the 'true darkness' he worked so hard to reattain ripped away from him, like his soul was after sleeping with Buffy.