I have a decent sized Deathwing Army. Terminator Captain (Counts as Belial), Terminator Librarian, 25 Deathwing Terminators, and 2 Landraiders (all of this fully painted) and I could take a third land raider (unpainted) if I needed it. I usually play against Eldar or Tyranids. When I go full Deathwing, I usually don't do too well. But that is probably due to several factors.
1) I usually play the same guy over and over (my best friend) and we know each other's play style too well 2) I'm probably not as good at 40K as a lot of you (even though I've been playing since 2nd edition, go figure) 3) It doesn't seem to be as mobile of a force as I want/need it to be. My friends Eldar run circles around me. 4) my terminators seem to be wearing tinfoil instead of ceramite for armor (I roll an inordinate amount of 1's for saves with my terminators, so much, that my friend sometimes counts that in as a factor when he's attacking them....)
That said, I'd love to see my Deathwing do well, but as it stands they usually perform best when I'm playing a fairly high points cost game and they are supported by other units.
As a side note, I do like to deepstrike them a lot and that kills my terminators just as much as it doesn't.