The hardest part of drawing Engy and Soddy are the helmets. I've drawn a lot of the Engy by this point, but without any of his headgear (for my upcoming TF2 story). You should see the earlier versions. The eyes should be more "squinty" on the Soddy - but it's not bad considering that is was my first try at drawing the character.
He's characterized by the over-sized helmet (or under-sized forehead, whichever) hiding his eyes and when I think about it, I should have gone with that - it certainly would have been much easier not to have to draw his eyes and browline. I'm trying something different though, and once I start dishing out small doses of "Respawn" I think people will look past these small differences since it's an origin-based story. There's only so much you can repeat (such as using exact angles on certain characters to keep them 'in character') until you have to just say "fuck it" and try to add something to make them work easier and more naturally in a story environment.