(or "You Knew The Job Was Dangerous When You Took It")
At some point during Season Two of 'Buffy the Vampire Slayer', it became obvious to the show's producers that they had a spin-off on their hands. Angel, Buffy's boyfriend on the show, was also a fairly complex protagonist in his own right, with a story that could easily become its own series. The idea of a (say it with me now) "vampire with a soul", fighting for his own personal redemption by doing good deeds...it's clever, it's got roots in popular culture ('Forever Knight' and 'Dark Shadows', for example) and it didn't hurt that David Boreanaz has some serious screen presence.
But if there's one thing that the eighty-three columns in this series has taught us, it's that a good protagonist is only the starting point for an ongoing series. Angel needed a setting, a modus operandi, a supporting cast, and some good antagonists...and they needed to give him all that without seriously disrupting the parent series. So what did they have for him? Cordelia, Buffy's sidekick's ex-girlfriend (who serves as comic relief and a damsel in distress, early on), and Whistler, a minor character introduced as Angel's old mentor. Then they found out that they didn't actually have Whistler after all.
As a result, the first season of 'Angel' does feel like a succession of false starts. Doyle is introduced as a Whistler-surrogate, then killed off (possibly due to problems with Glenn Quinn, the actor who portrayed him, although details are murky.) Cordelia then becomes the Doyle-surrogate, and Wesley, who was the Giles-surrogate for a while on 'Buffy', becomes the Cordelia-surrogate. (It's a running trend on both series that they introduce characters to act as the helpless victim who needs rescuing every week...then slowly make them more powerful and competent as they grow progressively fonder of the character, and introduce a new character to take their role of potential victim. So Giles is replaced by Wesley, Willow is replaced by Dawn, Cordelia is replaced by Wesley on 'Angel', and Wesley is, in turn, replaced by Fred. But I'm getting ahead of myself.) About the only thing that really seems to work right off the bat is Angel's nemesis, a law firm with a never-ending supply of evil called 'Wolfram and Hart'. This is a stroke of casual brilliance--by making the enemy a faceless corporation, they can establish individual villains, then dispose of them once they're no longer useful, all without getting rid of the central antagonist.
Other supporting characters show up as Season One progresses, but some find places on the series while others don't. Kate Lockley, a cop who discovers Angel's vampiric nature, never seems to really gel as a romantic interest and fades away, while Gunn, a street-smart vampire hunter, fits in quite well as a competent sidekick. By Season Two (and the arrival of fan-favorite Lorne, a demon with a nightclub and a karaoke obsession), you can see that the pieces are beginning to fall into place. More importantly, by Season Two, the writers seem to understand exactly what they're writing about, and what the concept of "fighting for his own personal redemption" means, and Season Two's storyarc is arguably the series' finest hour. (Well, it's more than an hour, but you know what I mean.)
Season Three seems to continue that trend, with Winnifred "Fred" Burkle added to the cast to replace Wesley as the smart-but-vulnerable one, but then they make a mistake that many a continuing series has made...they introduce a baby. Connor, Angel's son, is an interesting idea...but the problem with it is that creating a truly great storytelling engine is all about finding a point of balance, a setting that can generate ideas for stories without having to change the engine itself. And anyone who's spent any time around a child knows that they grow up at visible speeds. One day they're not walking, the next they are. One day they're cooing and gurgling, the next, it's "Mommy, give me milk!" A child can't be held in any kind of stability, not without making the series unbelievable.
'Angel' tries the time-tested trick all sci-fi/fantasy series pull, sooner or later, when a kid gets involved. Connor goes to a parallel dimension (the details of this handwave change, but the next bit is constant) and comes back all grown up and ready to become a regular supporting character. And that's when everything goes off the rails. Connor proves to be an unpopular addition to the cast, and Charisma Carpenter (the actress playing Cordelia) decides to leave the series to raise her own real-life infant (her pregnancy was worked into the series, but she can't send her child into a parallel dimension and pick him back up when he's seventeen.) Plus, parent series 'Buffy' is coming to a close, and 'Angel' is drawn into the events surrounding that whole mess. (And it doesn't help that many of the series' writers and producers are a bit busy trying to give 'Buffy' the send-off it deserves, and can't spare a lot of attention to 'Angel'.) The engine gets gummed up, and seems to stall completely as Season Four never quite takes off.
For the final season, they completely revamped the status quo, in ways that can best be described as "risky". Angel takes over Wolfram and Hart, trying to redeem it from within. Spike wanders over from the end of 'Buffy', which causes a problem as his character's spent the last three seasons becoming more and more like Angel (to the point where he also has a soul. As Angel put it, "I was doing that before it was cool.") There's a sense, almost from the beginning, that this isn't going to last. Sure enough, Season Five was the last season, and they go out in a blaze of glory, with many of the characters dying, and the survivors confronting the literal armies of Hell in one last, apocalyptic battle for the soul of the human race. The final line of the series..."Let's go to work."
And then they do. Remember the 'Buffy Season Eight' comics? The concept proved so popular that IDW decided to do an Angel Season Six in the medium as well. But unlike Buffy, Angel's finale didn't leave a storytelling engine there to work with, not even a radically altered one. 'Angel' ended with the Apocalypse. It's a little tricky to have a status quo after that, and sure enough, 'Angel: After the Fall' has so far been an exercise in picking up the pieces of the shattered engine and trying to put them together into a recognizable shape. Perhaps, once that's done, they can tell stories with the character again...but some finales are more final than others.