I think the graphics in the 6th installment should be simpler, for example, like in King's Bounty (simple, but with style), because in the 5th game, it doesn't look very good up close. And remove the large units. Make all units occupy one cell.
P.S. I've already written somewhere that it's annoying to manually rotate the camera around a hero who goes behind trees. Forget about this 3D map; it's better to have it like in the old games, without scrolling, so that everything is visible.