In short, here's what I think.
1) This needs to fix the death mechanic. It's poorly designed to mix undead and demons (and a mutation that isn't a demon or undead). I would replace the demons and mutation with more undead.
2) The sea is certainly designed even better than in game 5. There are even unique units (pirates, mermaids, and sea mutants), but I would like to see more.
3) I think the Chaos campaign has a very poorly thought-out plot. You play as some pirate faction, which is silly and completely out of place. This uninteresting campaign should be removed and replaced with a decent one, as it's below average.