IdeaVim is the uncanny value of vim for me. It's so close to being actual vim, but every now and then it does something unexpected and it completely throws me off.
I recorded a macro to change shouldBe([true|false]) to shouldBe[True|False](). Pretty simple: qqf(ds(~$a()<esc>q
But the vim-surround plugin emulation doesn't work properly with macros, so it'd get stuck and instead of just doing n@@ , I'd have to do n@@( , i.e pass the seperator I used for the delete surround command.
It doesn't have fold toggling, so z[a|A] doesn't work. The undo behaves weird, you usually have to do it twice UNLESS you've not moved the cursor since doing the last edit.
The git integration isn't as good as vim-fugitive and I constantly find my self reaching for the mouse to do anything git related, whereas in vim I could do it all with the keyboard.
The plugin gets brought up all the time when people talk about the JetBrains tools and no one seems to mention the short comings.
(intellij sometimes has recurring problems with lost keyboard input under linux+gnome. IdeaVIM is one of the first plugins i disable, when that happens. and it often helps.)