Things that really bother me:
Jack/Jonathan is a closeted homosexual— mkay. I know there’s the “D&J homoerotic overtones” school of thought though personally I never saw it- David’s life would have been a whole lot easier if he had been gay (it would have taken out Bathsheba and other troublesome wives).
Reverend Samuels- this is by far the worst misfire.  Eamonn Walker’s a good actor (loved him as Said on Oz) but the character is completely wrong.  Among other things he’s 30+ years too young; in the series as in the Bible he’s supposed to have annointed Saul- 20 years ago- when he’d have been about 25.   They should go more to the source: in the Bible Samuel didn’t just preside at a coronation, he basically stepped aside to let Saul rule because the wartorn Israel had been a theocracy with Samuel as first among equals of the theocrats, and this should have been the case in the show.
If you want a black actor the role screams James Earl Jones (or Morgan Freeman if you can afford him), a man who you can believe speaks with the authority of God and also who you can believe is ancient and has been through hell sideways since before 80% of the population was born but who at the same time is still vibrant enough to be at the top of his game.  I’d paint him closer to Harry Dean Stanton’s character (the Prophet Roman Grant) from Big Love except less corrupt (though no less frightening)- old and perhaps a bit frail but still vital and frightening, a man more likely to drive into town in a battered (but immaculately kept up) armored pickup with a brace of 9 mm on the seat beside him and an old coat and hat than a towncar driving guy in a suit and fur lined overcoat and drinks expensive Scotch.  He’s somebody you respect immensely but dread ever having to actually see, though at the same time when he arrives you are NOT going to keep him waiting; he was once literally and figuratively the Wrath of God incarnate and is still no man to be trifled with, less Barack Obama, more Jeremiah Wright, a John Brown type figure with a prophetic beard and fiery eyes.  (A Haitan actor might be good.)   Eamonn Walker does what he can with the script but you don’t sense his importance, power, holiness, and king-maker status.
Then there’s the issue of the Goliath tank. In the first place it shouldn’t have been called Goliath because that by definition alludes to the giant David killed- nothing else. Call it Gigantic or whatever. In the second place it shouldn’t be a tank but a new super weapon- Goliath was the most fearsome thing that the Philistines had after all, not one of 10 identical ones in a row. In the third place, David killing Goliath with a sling was a moment of inspired and comical brilliance, not unlike Indiana Jones shooting the swordsman- a “let’s cut the crap” “fightin’ means killin’” “I never heard a corpse ask how he got so cold” moment. David shoudl take out the enemy’s new Megatron with something simple like a sticky bomb or killing the operator and then turning it on the army behind it. Maybe if it was a moon sized battle station capable of destroying a planet but with a tiny exhaust port that if hit with a single torpedo from a small fighter craft could set off a chain reaction that… nah, that’s just silly.
And what’s up with that front line to begin with? That’s the most sissified battle front in history- 10 tanks? One airstrike dudes- I know this is an alterniverse but hasn’t it ever occurred to you that those planes you have can drop explosives? The tanks are shooting at your men so you’ve got ample cause to bomb them. (Another reason you need more than just a tank- something that even the aircraft would fear going near due to heavy anti-aircraft artillery that’s also taken out by David- the writers just didn’t think this one through.)
And the Franz Liszt reference… NOOOOOOOOOOOOOO!!! Making reference to 1846 (by definition “1,846 years after the birth of Christ, the messiah from the House of David”) is all wrong, completely takes you out of the continuity. There should have been no Franz Liszt, their dating system is alien (it’s the year 21 Silas perhaps, like the French Revolution- we’re given bits and pieces of the war but it’s easy to forget with the new city of Shiloh that there was a holocaust that happened here).
Personally I’d have had as the first scene Silas’s coronation, filmed (with a greenscreen of) a desolate destroyed city, then transition into the rebuilt Shiloh. Sets the stage.
Silas’s mistress— he was seeing her before his wife but they only had a kid 5 years ago (or whatever)? Better if he has illegitimate grown sons. Ishbosheth [easily transitioned to the Duke Seth] was a major figure in the Bible, and though he was a legitimate younger son it’s easy to make him an acknowledged pre-coronation illegitimate one who has no place in the succession until Jack/Jonathan’s death. The only importance of Saul’s concubine and younger sons was that David gave them over to be slaughtered and their mother (Rizpah) guarded their bodies til they decomposed, which I doubt will be an element in this (though I can see it ala Servilia’s death in ROME).
Anyway, I’m thinking far too much about this, but the point is that if I can tell you this megamillion dollar epic TV series is not going to work (except as a miniseries where it coudl be brilliant) why can’t the people who greenlighted it?