So this is an aggressive B/W deck that doesn't follow a particular format.  Personally, I'd add more control - black discard control and whatnot.  Mana base looks fine.  22 lands is light when you've got 4, 5, and 7 cost spells, but the dark rituals make this play closer to 24 lands. 

To give you a summary, I'd consider going more black & using more control via discard, improve the removal spells if you can, lower your creature mana curve, and use more aggressive W/B creatures and fewer non-aggressive ones.  Try to get more 2-for-1 spells. 

----Control----

Regarding control, if you don't want control, but just straight aggro - that's fine, disregard this paragraph.  Thoughtseize is about the best around, but very expensive.  Some cheaper alternatives: Inquisition of Kozilek, Duress, Despise, Cabal Therapy, Survical Extraction, Unmask.  I'd run 4x Hymn to Tourach (more on that below) and 8x spells like thoughtseize. 

Hypnotic Specter isn't bad either, with evasion & random discard, but if you go too far down that road, you'll start looking at Megrim and Liliana's Caress and you'll have a discard deck.

Gerrard's Verdict is a weaker Hymn to Tourach.  Your opponent will only huck lands if they're landlocked or they don't care about the lifegain, either way you're not getting ahead much.  Run Hymns instead, the random discard is much better than letting opponents choose, and you get 2 cards for 1. 

----Removal----

For removal, you've got 3 o-rings, 2 geth's verdict, 2 doom blades.  That's OK, but if you're not playing a particular format you can do better with removal.  Swords or Plowshares or Path to Exile beats any creature removal in there now.  Dismember is probably better removal too.  Fiend Hunter gives you 2-for-1, removal with a body. 

Go for the Throat is almost always better than Doom Blade.  For sacrifice removal, Gatekeeper of Malakir is better than Geth's Verdict - it gets you a body too.  Sideboarding o-rings is OK if you're planning to use them against planeswalkers, artifacts, or other non-creature permanents.

----Other----

Edge of divinity is going to give +3/+3, that's great for 1 cost, but running non-recurring creature enchantments is begging to be 2-for-1'd.  Slapping that on a creature puts a big sign on the creature that says "kill/bounce/burn me and you've killed off two cards."  I'd think seriously about tossing them. 

----B/W Creatures----

I recognize you picked B/W creatures to take full advantage of the Deathbringer Leiges.  They're great, but if that's your intent, I'd consider a few different creatures.  The Sillmoon Cavaliers are great, don't touch them.  The Putrid Warriors, Souls of the Faultless, and Vishskal should all go. 

Instead, Nightsky Mimic is 4 damage on T3.  Tidehollow Sculler can remove early threats from opponent's hands.  Orzhov Pontiff may be useful, I'd have to playtest.  If you do want all W/B creatures, you'll want another Deathbringer Leige or two, and I'd also consider 1 or 2 Teysa, Orzhov Scion. 

Vish Kal is cool, but costs way too much to be useful.  In an aggro deck like this, you should be done long before you've got the mana to hard cast him.  He might make a good EDH general for B/W, him or Teysa, but in an aggro deck he's dead weight. 

----Creatures Generally----

You need at least 2x more 1-drop creatures, maybe 4x more.  Sarcomancy & Carnophage are fast 1-drops.  Typhoid Rats, 1/1 with deathtouch rather than lifelink, fit aggressive play better.  Mother of Runes is pricy, but rightfully so, she's maddening to play against.  Doomed Traveler costs nothing and is  removal resistant. 

Blood Artist is best as a finisher in a deck where you can sac everything at will.  Killing Wave is one way to do it, cast for B and sac everything to finish your opponent.  Without a sac outlet, he's dead weight - no board presence, not aggro at all.  I'd also toss the Souls of the Faultless, they're awfully defensive for an aggro deck. 

Regarding the non B/W creatures, I'd be a little concerned by the Black/White Knights because they're both solid colored.   Think about some 1W & 1B drops instead.  If you're made out of money, Dark Confidant is to die for - card advantage wise - but who can afford them?  Nezumi & Oona's Prowler are good examples if you're doing discard control.  For white, maybe Cloistered Youth, Nearheath Pilgrim. 

If WW/BB mana on T2 hasn't been a problem with all the duals, there are better WW/BB creatures.  For example, I'd take Gatekeeper of Malakir over Black Knight any day - protection from white isn't a huge deal since white has less removal.  Nantuko Shade has great pump, Soltari Monk/Priest is very aggressive, Loyal Cathar is removal resistant, Bloodghast & Nether Traitor recur, etc. 



Hope this helps!