I have found the Wraithknight to be ineffective in most games. It's base point cost being what it is, with two guns that are great, but I haven't found anyone who has feared the guy. I've lost him in almost every battle, and that's with him hanging out in cover or something. I think he's lived in two games, and he's not a very big factor in those games. He draws fire, that's his best attribute. He's been absolutely destroyed be a swarm of Deamonettes, killed by a Trygon, and Land Raiders. His T8 means that his armor is often a joke, because whatever is going to hit him is going to ignore the armor. He's difficult to get good enough cover at times, so he's having to be screened. His two guns are amazing, but for 240 pts, there are a lot of times he just cannot kill enough to warrant his cost. If he's not shooting vehicles, or big bad monstrous creatures, he's not paying for himself. He's virtually worthless against horde armies, unless you buy the really expensive, let's make him 300 points variety, in which case I could have two wave serpents which deal much more damage.
Is he nifty? Yeah, he looks awesome. I bought one day one. However, I find myself not taking him in most battles at this point. If it's under 2500 points I don't even bother. There are much better ways to spend your points.