I'm currently working on a series called Greek Gods. It mocks Greek Gods on each episode, the first episode (planning to be released around September-December) will feature Hades, Poseidon, Ares, and Zeus. you can see all of the character design and such here: http://meltedtoons.blogspot.com/2010/09 ... cenes.html
the main thing (other than the feet which you know about) is that their hands look like frog hands... the little finger is the biggest on the hand - just shape those hands a bit more...
The only thing I see that I would change is maybe something to distinguish better between the Zeus character and Poseidon. Unless you're going to have Poseidon always pictured in water, visually he looks too similar to Zeus. I don't think the beard and the Trident are enough. This also could get kind of confusing if you plan on having even more gods. Perhaps, I know it's cheesy, but using different colored robes or hair to distinguish the characters better. When you look at the Hades character, you automatically associate him with the underworld because of his black robe. Or maybe you could use different colored halo effects around the crown.