I love my Chaos Dreadnought. He looks cool. Two close combat weapons, heavy flamer, twin linked bolters, and a nurgle-themed paint job. But as far as effectiveness goes, he's been a thorn in my side. I'd love to field him, but without a doubt, I've suffered so much every time I've fielded them. In my last two games, my close combat dreadnought has been less then effective. In fact, he's killed more points on my side then on my opponents side.
So, as much as I like the looks of him, I can't field him if I want to be effective. I played a small 1000 point game yesterday against space marines, and he was a waste of 105 points. Two rounds I rolled a 1, with the first round luckily not causing damage because he was strategically placed and troops were still in rhinos. A third round I rolled a 6, but since he had been immobilized, it didnt' do anything adverse. But he was immobilized by then anyways. The second roll of a 1 caused the death of two of my plague marines. That was fun.
The other problem is the predator. In the tyranid battle, it was taken out first round with no chance for survival. In the space marine game, he did some damage, but not much. The question I have to ask myself is if he was really worth it. He did take some fire, but did he cause much damage?
On a side note: Must remember to roll Warp Time checks at the start of rounds!