I can't remap my hot keys with it. Seriously, I'm left-handed. I don't like using WASD.
Also, I don't like the totally disorganized properties of entities. They have all kinds of disorganized, unplanned property names - some located in the flags tab instead of the main one, with names that are often confusing and not self-explanatory. And a lot are now defunct or do nothing. Many seem tacked on haphazardly.
Example of a good entity property:
CP Entity: "Can Blue cap this point? [yes, no]" Self-explanatory.
Example of a bad entity property:
"Choose Blue team role [1, 2]" (or something like that). Where 1 means Attacking, 2 means Defending (or is it the other way around?). You have to look it up on the Hammer Wiki. Should be "Choose Blue team role [Attacking , Defending]" - nice and clear.