They seem to be designed as an elite shooting army. Their CC is potentially powerful but I think they're going to be really hamstrung by I2. Lose a combat and even Guardsmen have a great chance of running you down, let alone Marines or (emperor forbid) Dark Eldar.
The only thing that might be an issue is that they are heavily oriented toward the anti-infantry side of shooting. Reliable anti-tank boils down to a pretty short list:
1. Triarch Stalkers - Assault 2 Multi-Meltas on a Move Through Cover/Living Metal Walker are no joke.
2. Scarabs (Entropic Weapons) - Drain the AV of your target(s) and then blast away with your abundant S4/S5 guns. I expect to see these a hell of a lot because they're the only real answer to huge parking lots.
3. Heavy Destroyers - Lascannons stats are nice, but at 60 points a pop and 1W, they're fragile for the price.
4. Monstrous Creatures - C'Tan and Canoptek Spyders can mess up tanks in assault, but C'Tan are expensive and Spyders won't do much at range besides generate extra Scarabs.
Other than that, their anti-tank options seem unreliable (Doomsday Cannon), one-shot (Tachyon Arrow), very likely to die shortly after making their attacks (Doom Scythes, Command Barges), or based on everyone's favorite Gauss rule.
Overall I think they'll put down infantry like nobody's business, but tearing open metal bawkses might be problematic for them. Still, I'd definitely rank them as a powerful army, they have a lot of potential to do a lot of things.
