What does game "depth" really mean?

The net effect of this is two things:
1) I don't care if the physics in Xonotic is "different" from Nexuiz, it just needs to "get out of the way" as it were...and let the action be fast....extremely fast

That's exactly what the current physics do for me. Nexuiz physics feel limiting to me, like with a handbrake. They have their good points though - they are a bit more intuitive at the start (the current CPMA-like strafe-to-turn-quickly is unintuitive, but also doesn't get in my way as I only use it for running, not during combat - during combat, I move exactly like in Nexuiz, even with the same keys pressed in the same way at the same time).

And generally I agree to your point. Depth means that you improve not by knowledge, but by "experience" - by getting used to faster and even faster action. Just, it is a lie that the current physics are way slower. In fact, with the current physics, I'd outrun you on any race (not CTS-only) map anytime, even while fighting. On racetrack I am twice as fast with current physics without even using the weird strafe-turning. On subseatrack I would estimate +50% to +100%, somewhere in that range.

One thing I am scared of with the new physics, is, how fast a jlue or a Red Dragon could potentially become in them. Especially if he also has a laser/mortar/whatever, he then can keep his speed much more than he could in Nexuiz, and be easily twice as fast as me with them.

BTW, by your definition, Nexuiz physics quite lack a lot in depth. They are mostly based on knowledge - you have to KNOW how to exactly turn your mouse at what angle to get optimum acceleration. Where this goes wrong, is when the "knowledge" gets transferred into software - namely strafebot, and then outperforms the best minds. What I want instead, is physics that are as fast as possible while an average player can still control it, and then let the good movers be even faster.

Other typical examples of what defines game depth, by your explanation:

• weapon combos - things you must experience in combat and cannot just learn in theory
  
• trick jumps where you have to plan ahead
  

However, none of this should be "enforced" by artificially restricting the game! Additional lag in the game sure increases depth, as your mind suddenly has to work much harder. However, it sure is nothing we should strive for. Depth is something that should not be enforced by weird restrictions, but by "extensible" game design, by making MORE possible!