Orgryn are big dumb brutes, and we love em for it. +10 Strength and Unnatural S (+2) is pretty handy for swinging a melee weapon around, and their high Toughness and Wounds (25+1d5!) make them damn sturdy. They're practically ghetto Astartes!
…except the Orgryn-Proof trait stabs them in the ass. They can never use a melee weapon better than a Mono- Great Weapon (2d10 Pen 2, Unbalanced) which is pretty lame in the long run. When your party gets up in the higher Logistics scores and start busting out the Bolt/Chain/Plasma/Power weapons, our big strong fella is stuck with a rather basic weapon. There's no way in the rules for a weapon to become Orgryn-Proof.
In essence, you have a big bruiser sort of character who really would be better off trying to figure out how to be shooty and nab an Autocannon even though he has three Aptitudes (Weapon Skill, Strength, Offence) built around melee. It leaves him with two options: be a tougher, less accurate Heavy Gunner, or be a melee character with a glass ceiling, forever trailing behind the Commissar or any kind of choppy Weapon Specialist. His chances of Dodging anything are about nil, he can't talk worth a damn, tests to shoot him are at +10… All he has going for him is that hefty stack of Wounds and his nice TB, and even that can't stand up to a full-auto barrage.