While they're at it, they could make the engine allow characters and monsters to knock each other off cliffs and improve the AI enough so that this couldn't be easily abused.
Oh, also, lava is really hot. Standing over it will burn you. Also, it will create an updraft that could be interesting during aerial combat.
Also, water flows around solid objects, not through them; the swim in The Crucible should tend to send you around obstructions. Also, velocity must increase around obstructions given a constant volumetric flow rate; you should shoot through the choke points.
Also, sinking versus floating depends on average density. Since a character's volume is roughly constant, it shouldn't matter what you're wearing; all that should matter is how much total weight there is between your person, your gear, and your loot. So if you want to swim through a tunnel and fight on the other side, you'd better hope the monsters can be dispatched with nothing more than one weapon and your jewelry.
Ya know, this is actually sounding pretty cool. Is there an MMO like this?