OK, here's my Expert Opinion.
Overall, it's a great start. It has a definite Zeerust flavor to it, as if it came out of BioShock. The arms are my favorite part; I like the girders and the elbow panels, and the little teeth at the ends. Great job.
I also really like the teardrops on the sides, and the arc where the upper armor meets the flanks. The FighterKiller turrets would fit in those teardrops nicely. However it is important that on the Lilith, those areas return to the iconic circles/pentagons of the original model, as the Lilith's Cluster Bombs are more deadly and have nice round shockwaves that match the launchers.
The nose needs more work, as right now it looks very basic. I like the idea of the Lilith having the tusks, and the Cain having more of a bullnose. Maybe smooth it out a little bit more, like the nose of BrandX's E-Wing.
Although the girders on the arms are appropriate, you did go overboard on the underside and flanks. You really should eliminate them, and find some other way to detail that area. Perhaps bevel those sharp edges connecting the red sides with the bottom panel, or completely re-invent the geometry there. The girders are OK in the little areas on either side of the engine slots.
Keep up the work. I'd like to see 'clay' renders with Ambient Occlusion, though, as right now the contrast is a little low and we can't make out the details.