Season 4 of Angel is bad, I agree. Starts out okay and ends with a bang, but I have a hard time getting through a large chunk in the middle of it.
But Season 5 of Angel is brilliant. I love that they flipped the premise of the show on its head, having Angel & co. take over Wolfram & Hart....
Spoiler
In fact, the finale of Season 2 of Luke Cage pulled an almost identical move, with Mariah leaving Luke in charge of Harlem's Paradise, to try to fight crime from within the corrupt organization.
There are so many amazing episodes: "Harm's Way" "Life of the Party", "Smile Time", and pretty much anything to do with Fred/Illyria. And it has Spike! :)
And don't get me wrong, Buffy is far from perfect as it is. We are currently rewatching it for the 5th or 6th time, haha, and we're on Season 6 at the moment. My husband really struggles with this season and how much "melodrama" it has, but even he admits that *most* of the episodes, even the ones that don't work as well plot-wise, still have good dialogue and really nice character moments.