Before TrueBlood, that was the case for me as well. I tried watching Angel, but could never firmly plant myself within its storyline.
Joss Weldon (sp?) really expanded on the cult film's premise. Not only would The Slayer kill vampires, but all demons. It was a great idea which helped put The WB on the map. Heck, I thought that UPN would run the show into the ground after The WB cut it loose, but Weldon tied up the series' final two seasons very well in my opinion.
The only thing I really actually held against the show was the killing of Anyanka in the series finale. In my opinion, if ANY character should have bit the dust in the end, it should have been Dawn. I never did like her "The Light" character. Why she survived the apocalypse and not Anya, I do not know.