I do love them.
In a universe dominated by horror, greed, and GRIMDARK, beset on all sides by gibbering abominations, vile heretics, and aliens of all stripes, you have the happiest damn race in the Galaxy.
Why? Because they've already won.
The Imperium wants to rule the Galaxy, as they see it as their divine right. The Eldar want to atone for their past misdeeds, hunting down the forces of Chaos, and trying to bring their race back from the edge of extinction. The Tau want to include everyone in The Greater Good, or kill them trying. The Necrons want to wipe out all life, but there's a lot of it.
The Dark Eldar are just here for the beer. The Tyranids, for the DELICIOUS BIOMASS.
And the Orks? They just want a fight. A "roight good 'un, too". And by The God-Emperor, they've got one. Seeing as everyone else in the Galaxy wants to fight each other, and them, and sometimes themselves, no matter where Orks go, a fight is soon to follow. They're living the dream - something that can be said of scant few people in 40k, never mind an entire race.
Yes, the generally take the role of the "comic relief", but a few of the Black Library novels show us that an Ork can be a credible, terrifying threat - my example...
Roan and his men dived into the trench - it would keep them safe from the gunfire, at least for now, but the artillery thumping nearer and nearer let them know they had scant time to enjoy their rest.
A few of the men (brave souls that they were) had taken up firing positions, bracing their lasguns against anything they could for a better shot at the enemy. Callis... was nowhere to be seen. The Heavy Bolter the Captain had slung him with would be of great use here, shielded from the worst of the fire, and directly in front of the advancing line.
Lunatics! They were charging through the No Man's Land without a care in the world! The men tried to take them down before they reached them, and succeeded in killing maybe a dozen - each of the beasts needing several shots to down. Roan had seen what a Lasgun can do to an unarmoured man, but the creatures wore little more than scraps of leather and the odd metal plate. They were bizarrely tough, taking shots to the face that would kill an average man, and yet they kept coming, screaming.
For each the men downed, five more took their place in the charge. There was no way they would manage. The Captain ordered them to fall back into the trench and prepare their bayonets - the fight was coming to them.
The first of the beasts threw himself into the trench. It was massive - the size of one of the Emperor's Astartes, at least. It wore a huge, roughly-beaten metal faceplate, wrapped around its jaw - it even looked like it might have been implanted into its face. And its expression... it was smiling, as it screamed an unholy, bastardised dialect that seemed strangely familiar. Its green skin shone with oil, blood, and a general waxy demeanour.
With a single swipe, it knocked Davin off his feet, and plunged a wicked-looking blade into his chest. The great beast laughed and roared as it continued through the trench, followed by his brothers. All larger than even the biggest of the Guardsmen, all wielding cruel-looking blades and handguns that looked ready to fall apart.They slaughtered the men, making sport of it - laughing as they killed, huge gouts of gore sending cheers through the advancing tide of green.
Roan had sought to escape from the onslaught, and hopped out of the trench, running blindly away from the enemy. He had feared the Commissar would have him shot, but looking over his shoulder, he saw a massive metal claw, easily the size of a Lascannon, sweeping through the air out of the trench, followed swiftly by the top half of Commissar Jenkins.
To this day, the last words he heard would haunt his sleep, marking every minute of every day...
"LOOK LADZ, I GOTZ DA HAT! I IS DA COMMI-TZAR NOW, SO YOU DUZ WHAT I SEZ!"