Don't forget to include on the list: adequate hot water to mix in with the cold water.

I've had a few ridiculously cold showers at some hotels. Last year it was some Chicago-area Ramada which was completely full -- so given my very early morning flight out of ORD and untimely discovery of the issue with the shower (but less so with the sink), changing hotels was not an option.

Another thing with some hotel and airline lounge showers which I would rather not see: showers that require being reactivated every 30-60 seconds or perhaps every couple of minutes to get the water to flow again.