This one is addictive, not so much as HR for me, but still
The whole trick to this seems to be getting comfortable with ANY of the weps (machete included) and using their ammo as sparingly as possible (single shot mode, no automatic) until a better or at least equally good wep (depending on your situation) arises. Be OK with running out of ammo and using the machete, get the timing of the swing down, and in extreme cases this should be the only wep you use on full-auto. It's not a bad wep in close quarters, and does serious damage if wielded well.
NEVER stop moving, even if it's inch by inch. Clear the screen in one direction (unless there's a big yellow guy and your wep is weak) all the way to it's end, then go back the other way clearing as you go, keeping a sniper mentality (one bullet, one shot, one kill, use as little ammo as you can to kill as many as possible). Sometimes you get boned and get stuck with a handgun in a crowd, fire away on both sides till it's empty, swing away with the machete till a wep appears, and if necessary, dash through a crowd to a clearing to use it. At 1/2-full health, a few crowd hits is manageable.
What you want to love, in order:
Mini-gun: Slows you down, but cuts down crowds like they were zombutter. WILL clear to screens edge, even clears past that. If a blue gets too close, your chances of shaking him with this wep are slim unless you're fast with a turnaround shot, use that missle/airstrike/helicopter gun and save your ammo while it's firing. Again, stay away from full-auto, tap the spacebar and fire bursts.
God's hand: If you've ascended, meet your new best friend. Upgraded machete, limited uses, but everything it touches dies.
Flamethrower: Torch a crowd in a single pulse. Damage seems to be distributed when multiple yellows are in the line of fire, may require additional pulses. DO NOT use with the button held down, as fuel goes fast. Single burst, move forward till you're almost touching the lead zombie in the next crowd, pulse it once, repeat.
MFG: Clears everything in a single direction, offscreen included. Slows you down like the mini gun, and is only effective from it's tip forward. It's basically a 5 shot reset button, 2 shots in one direction, 3 in another (alternating sides), then pray for a good wep to drop.
Riot shield: If the MFG is a reset button, this is pause. Wield it only when something is close enough to hit, or solid on to push a crowd back from a crate. Keep a close eye on ammo, when it's gone, it can be big trouble if you're not ready.
Assault rifle: Large magazine, capable of mini gun damage with 2X damage power up, and a lead shield on full auto. I'd take anything above over it, but it's still a good one.
Shotgun: Only this low because it's situational. Capable of taking out multiple targets, or heavily damaging one. Use like the Flamethrower, get as close as you can to the leader of the crowd and buck off. Reload time is a nightmare when blues get close, but a short muzzle gives it close fire capability.
Sniper Gun: Can be a pain, or a life saver. Capable of shooting targets off screen, hits multiple targets in a single shot, and packs a punch on anything it hits. Reload time like the shotgun, but no close range kills. Targets must be tip or further away to take damage, so if there's a crowd, keep it on automatic fire and RUN, something better should pop up soon, and your clearing a hole in front of you.
Dual pistols: Gotta have one to get two, but two beats one any day of the week and twice on Sunday. Ammo expends faster than you think, but hard hitting to a single target. Full auto can soften a crowd nicely, and the shortest attack range save for the machete
Pistol: Either you see another pistol close by, you know you can expend the ammo in time to get the wep next to it too, or you've run out of options. Strong on single targets, but won't last long. Avoid if possible, the machete kills faster.
Machete: Last because it should be. A VERY efficient weapon that hits multiple, close quarters targets simultaneously, medium reload time. You can go a long time with just this, but try not to, having any weapon is marginally better than this unless they're right on top of you. Useful for clearing a hole to use your next weapon in. Get comfy with it, you never know when you'll need it, or when for that matter.
Final notes:
If you don't have both martyr trophies and the ALL of the machete kill trophies, work on em. Learning to deal with the bare minimum reduces panic later, and results in higher scores immediately. If you complete these two trophies, the rest will unlock soon, I promise.
Make sure to fire evenly on both sides when they're starting to close in. Taking down one side will only trap you in a corner, buying time in the middle of the area gives you the best chance to get a better wep/a health crate/2X damage.
If you're about to switch weapons, fire off all the ammo you can from your old one and THEN pick up a new one. Every kill counts, and so does every bullet. Expending the ammo from one will save ammo in the next.
Health crates and 2X damage crates do not go away if you don't pick them up. Use the health crates only at 50% health or lower, and use the 2X crates only when you have the assault rifle/sniper gun/pistol/dual pistol/shotgun.
To extend your kill combo, work all the way to one side, pause, shoot the next zombies coming on screen from that end till the other side has enemies, then work back to other end. Repeat.
Avoid trading down the wep list, trade up when possible. In a pinch, anything is better than nothing though