To be fair, Go for the Throat was already going to be a bit of a staple, given that it's a less restrictive doom blade in the right environment. Also, I'm not sure how much of Karn will even be seeing around tourneys. He doesn't seem too competitive to me. (Although the ability to exile any 2 permanents, given defense, in any color does seem good enough to consider running him) Lastly, I'm also a bit skeptical when it comes to the new Negator. I won't repeat the entirety of the discussion I had on Salv. but I believe he's basically an unblockable 5/5 or an awesome ground stall- neither of which necessarily generate ca in the same way Grave Titan would and, regardless of which role he ends up playing, you've got to go mono black to get this guy down on turn 4.
Of all the spoilers, my favorites, as an EDH player primarily, are:
"Spawning Shell"
Rare
3P
Artifact
(P may be paid for with either G or 2 life.)
1P, T, sacrifice a creature: Search your library for a creature with CMC equal to or less than the sacrificed creature's. Put that creature into play, then shuffle your library. Play this ability only when you can play a Sorcery.
(which really needs to lose the sorcery speed restriction

)
Puresteel Paladin
Rare
WW
2/2
Creature - Human Knight
Whenever an Equipment enters the battlefield under your control, you may draw a card.
Metalcraft - As long as you control 3 or more artifacts, equip costs of equipment you control is 0.
An equipment enchantress that can negate equip costs? Awesome!
Caged Sun
Rare
6
When Caged Sun enters the battlefield, choose a color.
Creatures you control of the chosen color have +1/+1.
Whenever you tap a land for mana, add one mana of the chosen color to your mana pool.
Another Lens/Gauntlet/Mana Reflection/Mirari's Wake effect.
Karn the Released(?)
Mythic
(mana cost) 7
Planeswalker - Karn
+4: Target player exiles a card from his or her hand.
-3: Exile target permanent.
-14: Set aside all non-aura permanents exiled by Karn, then restart the game. After that, put into the battlefield under your control all cards set aside this way.
(loyalty) 6
Yeah, I may not buy the extreme levels of hype some are, but I definitely think having answers to every permanent type in any color deck is nice.
and my favorite by far is
Praetor's Grip
Rare
1BB
Sorcery
Search your opponent's deck for a card and exile it facedown. While it's exiled this way, you may look at it and play it as though it were in your hand.
In a singleton format, this is amazing. Deny your opponent their Primeval Titan/bomb of choice until your ready to play it, steal a counter spell if you're in ub and need to cover something, strip out a combo piece, etc. Great utility for its cost.