When you've levelled enough, the Giants at that location are fantastic for soul farming at about 600 a pop.
Well, I've finally managed to do away with Four Kings. What's ironic, is that I'd forgotten to go offline and was invaded about half way through a run through the Ruins and was mauled savagely to death by some geezer just before the fog gate. The chap responsible was contrite for some odd reason and sent me a message requesting to help with the Four Kings fight. I accepted somewhat perplexedly, but alas, didn't find the sign at the agreed place.
Not to be denied, I went in again alone…
Spoiler – My basic Four Kings method
It pays to keep very calm during this fight with some good stamina regen of some kind. (I used Green leaves)
If you're melee oriented, try to get in very close to the first wraith and just time strikes with your best weapon and strafe around it. Don't rush (as I was initially prone to do) and try to keep the other kings if they arrive, in front of you but at a distance so that you can see what they're up to. I found the more spread out they were, the easier they were to take out individually, so a tactical retreat here or there to take stock of the situation (for estus) can help. Eventually, it'll fall.
Thus, it seems I'm on the home straight now. I'm seriously considering leaving the remainder of the DLC content for a second playthrough, although I probably should farm some more titanite chunks to upgrade my weapons and armour more, as I have a crapton of unused slabs of various kinds. I'm sure I'm going to need them for the final boss…
P.S: Congrats to GBG for the epic shirt-popping Street Fighter 2 moment. Must have felt good!