Even though I watched Seasons 1 and 2 of Angel, I never wanted to watch Season 5 and I continue to pretend they never resurrected Spike. Even though he is my favourite Buffy character, I sort of like that he dies, it is the perfect end to perfect character development. He is complete.
Angel is set in LA and takes place at the same time as Buffy. Various characters from Buffy make appearances, such as Buffy, Oz, Willow, Harmony, Drusilla and Darla (though some of these only appear once or twice). Cordelia and Wesley are main characters and so is Spike in Season 5 (the final season, which aired after Buffy finished). There's some coordination between plots. At the end of Angel Season 2, Willow turns up to tell him Buffy is dead.
As for Angel, I watched Seasons 1 and 2. It was ok, a bit silly I thought and not as good as Buffy. But then, I never like the character of Angel anyway, and I have friends (mostly guys) who prefer Angel to BTVS.
The ubervamps were called Turok-Han.
And you're right, they didn't kill "The First" as its the essence of evil, existing in every single person, and so is unkillable. Bringing Buffy back to life destroyed the balance of good and evil, allowing "The First" to attempt a seizure of power. When they defeated it, they basically restored the natural balance, forcing evil back into its rightful place, from which it is unable to try and take over the world.
Elena... She's ok. But she needs some flaws. We've never seen her do something really bad or intentionally hurt somebody. And the way she's so willing to die is too heroic, its unrealistic (I agree with all the posts before that Buffy was better). She's too good at the moment, she needs a dark side. Now, if she started getting involved with both brothers at the same time (a la Katherine) that would sure dirty her up a bit. But I don't see that happening, not for a while anyhow.