I can think of a couple of items right off the bat..
- no mouse wheel support - code navigation shortcut keys non-existant - ide crashed all the time - I can't think of anything else really because it's been so long I was forced to want to kill myself (translation: It's been a while since I had to use the VB6 toolset)
I would argue you never spent any serious time in the VB6 ide, because it was (is) complete garbage. The fact that people still use it proves to me that those people simply don't know any better.
And if you throw the argument that VB6 is great for just banging out windows apps that work, Delphi is a far better choice.