In the opening episode of the new Amazon series “Goliath,” Billy Bob Thornton, playing a Los Angeles lawyer who has seen better days, snaps: “I used to handle 20 cases at a time. I think I can handle two.”

Was this David Kelley, who, with Jonathan Shapiro, created and wrote the show, getting in a little dig at himself? You could imagine — actually, it was hard not to imagine — Kelley saying: “I used to handle three shows at a time and write 50 or 60 episodes a year. I think I can handle a 10-episode web series.”

As a group, the most successful of the old-school broadcast-network producers — people like Dick Wolf, Chuck Lorre and Jerry Bruckheimer — have resisted the lure of the streaming services. Kelley used to be in that league, but his last real hit was “Boston Legal” eight years ago. So when “Goliath” was announced, you could hope that the creative freedom offered by a short-season online production (which Amazon took straight to series, without requiring a pilot) would have a rejuvenating effect. Through two episodes made available early, the jury is still out.

With “Goliath,” which became available in full Friday, the prolific Kelley, a former lawyer, returns to the legal drama. (It’s the seventh he’s created.) He also returns to Los Angeles, the setting of the best show he’s been associated with, “L.A. Law.”

It’s a David and Goliath story, as the title half-indicates, though the main character, Thornton’s Billy McBride, is definitely the David. The action begins with a series of quick scenes establishing how down and out he is: released from jail, missing a court date, told to shape up by his teenage daughter, sitting on a beach-side bench and pulling a bottle of whiskey out of a paper bag.

That opening is promising — quick, textured, with a sense of place and a reliably prickly performance from Thornton. And as the story unspools, the part of it in which McBride figures continues to be entertaining, in a been-there-done-that kind of way — it’s reasonably well-executed Los Angeles noir, shot on picturesque Santa Monica and Venice locations, and carrying just the faintest echoes of John MacDonald and “The Long Goodbye.”

But then there’s the other half of the show’s odd bordering-on-bizarre split personality. The Goliath of the story is a behemoth of a law firm where McBride was once a partner; whenever the scene shifts there, the tone and rhythm change. Suddenly, we’re in an arch, slick, hyped-up TV legal show, with lawyers marching in formation and exchanging withering put-downs. The staff includes a dragon-lady associate (Molly Parker), a faint reminder of “Ally McBeal”; and a young lawyer (Olivia Thirlby) with an anxiety disorder who stutters in court.

In contrast to Thornton’s naturalistic portrayal of McBride, we get William Hurt breathing hard as McBride’s nemesis, a ghoulish figure with a scarred face who sits in a red-lighted room watching surveillance video of his employees. Clearly, Kelley and Shapiro are trying to accentuate the contrast between their David and their Goliath, but they have ended up with what feels like two different shows.

That’s one miscalculation. Another is the needlessly complicated structure of the initial episodes. The nature of the case McBride has taken on (involving a suspicious suicide) is revealed slowly and cryptically, a bit of writerly delayed gratification that keeps your attention but isn’t particularly rewarding. Then, presumably because the first episode leaves so much unanswered, the next jumps back in time to fill in the history of the case — and when the second episode ends, the story hasn’t even caught up to where it started.

The narrative juggling has the feel of stretching — of starting with a story suited for an episode of traditional TV or maybe a feature film and extending it to more than nine hours. Final judgment on that will have to wait for all 10 episodes.

Some things we can probably count on, though. Kelley and Shapiro (they worked together on “The Practice” and “Boston Legal”) will serve up a snappy piece of dialogue every few minutes. Thornton, even in one of his more routine performances, will be a pleasure to watch.

And while many of the actresses have trouble animating their slightly cartoonish roles — Parker, Thirlby and Tania Raymonde as a combination prostitute and legal secretary — Nina Arianda will continue to be the best reason to watch the show. She’s fearless and hilarious as the low-rent lawyer and real estate agent who drags McBride into the case. When she deadpans, “He’ll be here, the hooker just texted,” it could be “L.A. Law” all over again.