Admittedly, it has taken a few false starts to get the beast into a position where a) he wasn't killed by a barrage of poisoned weapons; b) wasn't killed by a barrage of S8 AP2 weapons and c) wasn't neutered with his Suncannon by small, widely-spread units.
The fourth time is a charm and I found my Guide-blessed WK facing off against two Land Raiders. Now Ruby will complain that I didn't Guide his Riptide but if you're going to roll a 12" scatter not once but twice in as many games, you don't deserve to be Guided. Anyway, Guide ensured that both shots hit and rolling 5 for armour pen then 2 for damage meant Land Raider 1 was out of action for a turn. Turn 2 brought the second Land Raider close enough for another two shots from the Heavy Wraithcannons and another pen - a charge and 5 S10 attacks finished the job with the resulting explosion not even scratching the WK's paint (but poison weapons can kill it - sad but true). Turn 3 was a brief interlude where the WK went to help out the Scorpions killing a squad of Marines before it jumped back to Land Raider 1 to remove the remaining two hull points and cause another explosion. All of this for a single wound lost.
The only change from the standard WK I would considered would be to possibly take the Ghost Glaive (noooo I hear you scream) and more importantly, Scatter Shield for the 5++. Other than that, the WK has finally earned its cost (both points and hard earned moolah).
I'm interested to know how others have used the WK to good effect (Sun Cannon against tightly grouped Necrons aside GW).