Khorne, not to be confused with a vegetable, is the good of blood, rage, and skulls. Apparently, he's also the god of never reaching combat because he's so fucking slow.
So, let's do a mono Khorne army. Khorne units all rock in combat, but most of them don't move faster than infantry. That can cause all sorts of problems in a deep striking assault army. Khorne has up to 3 units that can move, Bloodthirsters, Flesh Hounds and maybe Daemon Princes. BTs and DPs are expensive, while Khorne Dogs are the only Khorne unit without power weapons. Bloodletters are murder machines, but not very tough and painfully slow. Bloodcrushers are solid bricks, but they move about that fast and have nothing to stop Dreads. All shooting comes from Death Strike, a plasma pistol that doesn't kill you. Things aren't looking good on the anti-mech front.
Mobile armies are going to run circles around you. You can handle this two ways. The first requires you speed up as much as possible to catch your enemy, sacrificing killy-ness and durability.
Speed Metal 2000 points
2x Bloodthirster - Unholy Might, Blessing of the Blood God
3x 8 Bloodletters
3x 10 Flesh Hounds
3x Daemon Prince - Wings, Unholy Might, Iron Hide, Mark of Khorne
5 flying MCs, 30 cav models, and requisite scoring units. I'll tell you, I'm not too sure about this. It's ridiculously front loaded, but even then there are problems inherent to pure Khorne. The DPs can do a lot of damage, but they are stuck with T5. Only 24 Bloodletters is pushing it, they will have to just drop into cover and hunker down. Still, even a few Bloodletters can clear an objective late game, and with 8 extremely mobile units running around it'll be hard for anybody to spare enough dakka to gun for them. Death Strike is an option to suppress lighter armor, but since everything flies and DS is so expensive, sacrifices have to be made. Karanak and Fury of Khorne would help the Hounds, but that'll either sacrifice unit count, reducing chances of hitting armor, or stripping options from the DPs or BTs. Going from base S8 to S7 can be all the difference if you go up against T4 multi-wounders or T6 MCs, and S6 to S5 is a big drop against basic troops as well as MCs. This is really cutting it as lean as I would like, leaner actually, but the basics are there. I'd be hard pressed to run this at lower points, probably by dropping Flesh Hounds.
The other option is to just flood the board with your slow stuff that nobody likes charging. Give him no way out, then step on his throat.
4x Herald of Khorne - chariot, Unholy Might, Fury of Khorne
3x 2 Bloodcrushers, 1w/ Fury of Khorne
2x 8 Bloodletters
3x Flesh Hounds - 10
3x Daemon Prince - Iron Hide, Mark of Khorne, Death Strike
Ok, this one is tricky. The only mobility comes from the Flesh Hounds, which are indeed fragile and not all that killy. DPs are your only shooting, accurate S7 on rear armor can maybe destroy something or more likely stall it for a turn. Of course, if it's in 12" stunning is all you need so you can munch on it.. The name of the game here is area denial. Pretty much everything is tough and killy in CC, so you set them up around objectives and force your opponent to take them. You have no support beyond Flesh Hounds because everything is so slow, so you'll basically pick a place and draw a line in the sand. Khorne units in Khover are hard to Khill, so use that to your advantage. Against an army that is slow, like Orks, you will munch them. Flesh Hounds either end up going after mobile shooters picking you off, or as a mobile reserve to reinforce areas that need help.
So that's Khorne. Khorne units are all great individually, for the most part, but they really don't mesh together to create a cohesive army. Unlike Slaanesh and Tzeentch, that can actually operate solo, Khorne really needs support from other units to make up for what his units lack, namely mobility and firepower.