Also, Golurk suffers from the fact that its most powerful physical Ghost STAB has a base power of 60 (though Iron Fist raises that to 72, which still isn't that good) though at least Earthquake has a base power of 100. Golurk's defenses aren't that amazing, 89/80/80 defenses aren't exactly great compared to 58/145/105 (Cofagrigus) or 48/135/135 (Dusknoir), but it's still pretty decent. However, what sets Golurk apart from other spinblockers is that it can actually do quite a bit of direct damage with 124 base Attack, as opposed to Dusknoir who usually has to rely on Seismic Toss or Cofagrigus who has 95 base special attack.
That's part of the reason I stuck with Golurk over Dusknoir. Like you said, Shadow Punch is a mediocre STAB for Golurk, though I will note, while 72 Base power isn't great, it makes it the strongest physical Ghost attack, with the exception of Shadow Force. STAB makes that 108 base power. Leftovers Golurk can take off 48.6% - 57.2% on a Calm Mind Cresselia, and if for some reason you want to slap a life orb on him, 62.6% - 74.3% with Shadow Punch, just to use as a baseline for the kind of power that Golurk carries. But fortunately, while I do believe Golurk's typing is poor defensively, I believe it is great offensively. You also get Earthquake as a STAB, which takes a 100 base power attack and turns it into a whopping base power of 150.
That said, I think Focus Punch is a great choice for Golurk. The lack of STAB is somewhat compensated by Iron Fist, which stacks with it. 150 Base turns into a comfortable 180 Base Power with face-tearing results. Ghost/Fighting also gives it good coverage; with ground providing a comfortable stab.
That said, Golurk is most effective when being dropped into a pokemon that can't do much with it, and encouraging a switch into a pokemon that can handle it more effectively. The two big sets I often see are Rock Polish and SubPuncher, who both benefit greatly from that switch out. Rock Polish can take a max speed EV Adamant Golurk to a solid 418 speed, allowing it to outrun anything Scarfed with less than 78 base speed. I prefer SubPunch over Rock Polish, however, due to the fact that certain priority attacks, such as Aqua Jet, Sucker Punch, and Shadow Sneak, are super effective against Golurk, and as you pointed out, it's bulk is nothing to brag about.
Now, once we get DW Golurk, the entire ballpark changes once we get a No Guard ghost type with Dynamic Punch, Stone Edge, Rock Polish, and Earthquake. Give it a priority attack, and we have our Ghost-type Machamp.
-Jesus-
I love CB Golurk and have been meaning to try out Rock Polish. He'd be even better if he got Shadow Sneak though, arg.
Wouldn't a fast Golurk be a good switch to Rhyperior? He shrugs off Stone Edge, Megahorn, and Hammer Arm, then can just EQ it or Sub if it tries to set up.
Kiiinda. I played around with CB Golurk, and while he is stealth rock resist, allowing him to switch in a lot, that set was a little to high-level for dumb old me. The hard part is predicting the switch in, if it exists, and because Golurk is fairly unknown, he is like Eelektross in that people underestimate him. Which makes predicting opponent hard, at least for me.
As for dealing with Rhyperior, it varies. If it has Stone Edge, Megahorn, and Hammer Arm, great! SubPunch Golurk takes 29.8% - 35.3% from Stone Edge off the physical attacker set, and forces Rhyperior out. The problem is that Golurk can 2HKO Rhyperior, and if that Rhyperior has Earthquake. The same set, using Earthquake, hits Golurk for 59.9% - 70.7%, which puts Golurk in the 2HKO range. While it is faster than Rhyperior, switching into a resisted attack is risky for the giant robot pokemon. I find that it is perfect to punish choice pokemon, such as those damned electric and bug types running around.
As an added bonus, it is immune to Thunder Wave. Take -that- you freaking walls.