Underwater content could be fun, wonder if they could get the physics right for it? Slow attacks because of the density of the water. but in saying that argonians being amphibians would have a nice racial advantage, extra swim time from extra breath and better combat for them underwater then the rest of us.
Plenty of sea wrecks around the coast, and it would be nice to actually kill those damned slaughter fish.
But then certain classes would be limited. no spell casting because you cant cast spells, (if the mechanics suggest spells are cast using verbals) I cast my.... blub blub lubub bl bub bllb blire bluuub blbub ball
Could also be used for getting out of line of sight for people using range combat from the bank if they cant see you.
Loads of reasons why to have and very little why not.