I am in shock that people don't "get" Willow and Tara - the instant Tara looks up and sees Willow in the Wicca group meeting, I felt breathless because I just knew.... gosh, I remember how exciting it all was watching it for the first time, waiting every week for the new episodes... The internet and spoilers ruin everything now, but back then everything was 
And I thought Willow as the Big Bad was completely believable... I actually enjoyed S6 immensely, it was a shame S7 ruined pretty much everything (only redeeming quality being that Faith was back). I think you need to know what it's like to be on the edge of sanity to "get" how easily that could be someone grief-stricken and power crazy. Jeez, if I'd had loads of magick when my ex dumped me without a word of explanation after six years, I'd probably have gone batshit mental and tried to end the world too.
The Spike soul thing always confused me... I, too, thought he was tricked, but upon further reading online I see that JW carefully wrote Spike's words to appear as though he was going to get his chip removed (the audience would naturally think that as he was always banging on about it), but actually he wanted to prove himself to her, that he was worthy of her.
It's interesting how I never liked the Spike/Buffy relationship upon first watch as a teenager, but as an adult I think he is the best. Ever. My perspective changed in a lot of ways, actually...
Never watched beyond S2 of Angel so think I will need to do that now thanks to previous posters recommendations - is it on Netflix? (And speaking of, Faith is redeemed and has a lot more character development in Angel, I love the episode where they broke her down, just so powerful, amazing writing).