Oooh, I honestly haven't considered what to run /against/ my KDK, I've been having so much fun running them. Honestly, KDK are a really flexible force who can summon new units in wherever they need, are very mobile, and favor MSU... tough to face, in a good player's hands.
One thing that immediately springs to mind for me is the near-total lack of AP2 in KDK choices--almost everything less than Bloodthirsters is AP3 or worse (or, alternately, is very expensive/very slow/etc, in the case of Axes of Khorne or power fists who are hard to fit into lists on people who deserve them). Mega-Nobz would be hard to shift, apart from by sheer weight of numbers of attacks (which KDK can bring to bear, in all honesty, but--every turn after the first that KDK units are stuck in, they're underperforming, since they pay for all those charge-only bonuses)... though yeah, if most of the enemy list consists of Maulerfiends and a Bloodthirster, I see how they might die fast. Sorry, will try not to consider the lists I field so much.
Bloodthirsters are honestly quite fragile, after you remove the Greater Rewards that Codex: Daemons had to offer. They have to sit on the ground out of combat for a turn before they can get stuck in, so if you have any shooting to speak of (say, 2 squads of Lootas on opposite sides of your deployment zone so as to provide a solid crossfire and deny it cover to hide behind). They're tough to hit in close combat... but don't, IIRC, have Assault Grenades so if you can make them assault you in cover, so much the better. Worst case scenario he'll be striking at the same time as your power klaws take a chunk out of him. If you can bait a Thirster into attacking a unit of a few minis (or multi-assaulting with other KDK units) so they'll wipe it out utterly, so much the better, since then you get another shooting phase while he's not stuck in.
Also, try to make sure he assaults you on his own, so that even in a challenge the rest of your boyz can pile in and heap their attacks on. At T6 3+/5++, he'll get chipped down to the ground eventually. Honestly, I myself don't field Bloodthirsters because they're such a points-sink for how fragile they are, even if they can unleash quite the can of whoop-ass... if they ever get stuck in.
Your opponent is capitalizing on the strengths of Daemonkin mobility with multiple Maulerfiends and biker squads (be thankful they haven't expanded into Gorepacks with squads of cheap MSU flesh hounds and bikers, to boot!), but that means you know what to expect from him. Tankbustas should make pretty short work of the Maulerfiends, who only have a few low-WS Attacks--and tankbusta bombs don't care whether your opponent is bringing lasher tendrils or not! (though I imagine Lasher tendrils would mess up a mob of Boyz something fierce--do take note of any of his Maulers he fields with them and try to shoot/tie up those ones immediately, since -2 Attacks on a whole mob in a large brawl would, I can only imagine, be hellish). Too bad orks don't have access to grav, since that's more or less the bane of Maulerfiends--fast walkers, immobilized after a single 6!
The Bloodfeeder... well, it starts the game as an over-costed power axe. If you can lock down the Lord with heavy hitters before he can chow down on a mob of Boyz to buff his weapon, you should be sitting pretty. Chase him down with Mega Nobz in a trukk, Biker Nobs, or challenge him with your Warboss early. Failing that, treat him like the Bloodthirster (albeit with a retinue he can shrug wounds onto)--shoot him to death.
One strength of the KDK list is the Blood Tithe mechanic--but how to play around that, since it rewards the opponent for you killing their units? Well for one thing, it only goes up to 8--in games of 1850 points or more, there's a very real chance that you'll be able to spill over that count of 8 BT points in 2 player turns. If he kills a lot/loses a lot during his turn, try to deny him future BT points by overloading his kill-tally for that turn. Turn 3 tends to be when I get overloaded, playing KDK, I find--if T2 you manage to reduce a lot of his units to a mere fraction of their strength without quite destroying them, you might be able to mop up on T3 for maximum effect to minimum enemy benefit.
KDK lists really don't have anything meaningful in the way of shooting, so you might be able to load up in wagons and let yourself get assaulted (just not encircled) with some of your units for a virtually free counter-assault--he wrecks the wagons and you pile on after. Alternately you could try disembarking behind your vehicles and "circling the wagons" in a sort of, uh, pseudo Rhino-rush wall that nothing of his (barring the Thirster) can get over. He spends a turn wrecking your vehicles, then you get all the important assaults. Warp, that might be a bunch of blood tithe points for his T2 (all those vehicles) so you can over-glut him properly on T3, like I mentioned earlier. Though sacrificing all your late-game "zip onto the objective as a scoring unit" cheap transports might, uh, not be the very most strategic choice, sometimes--this is all theory-hammer.
Honestly, when playing KDK, I try to press for playing Maelstrom missions rather than Eternal War missions--the MSU mindset of KDK makes kill points a hellish notion, plus the sheer number of FA slots that my own MSU lists bring, to say nothing of how many HS slots all those Maulerfiends eat up for the Scouring and The Big Guns Never Tire, respectively... it kind of feels like meta-gaming, but if you can get the edge on your opponent in half of the Eternal War mission formats right out the bat, you might be sitting pretty. At the very least, insist on rolling a D12 for both Maelstrom and Eternal War rather than settling on a D6 for one of them.
Plus, well, KDK's summoned units are perfect for grabbing late-game objectives when you draw "claim X or Y objective". If your opponent pulls this off multiple turns in a row, once all your units are committed elsewhere... you'll see how forgiving KDK are for the Maelstrom format. With Eternal War, at least your opponent can only jump on objectives at the end of the game, rather than summon a unit on whichever objective they need for a point every single turn. I honestly feel bad for giving away this secret of KDK players, but... hey, you asked for help, and that's what I'm here for. Basically if you don't play Maelstrom, KDK is fighting an uphill battle.
Hope that this has given you some food for thought! It's been fun approaching my luvverly bloodfiends from the opposite side of the table, for once!
What sphinx of plascrete and adamantium bashed open their skulls and ate up their brains and imagination? Imperator! Imperator!