Briefly, the problem is that it thinks you're holding down the keys (lag adds time between key-down and key-up events) so it repeats the letter you're "holding down." You can disable key repeating for this guest's console by changing how long a key must be down before it's repeated. There's a handy post that explains editing the .vmx file .. but I prefer to do it in the vSphere client:
- Pop into the vSphere client and "Shut Down Guest" (I know, sorry.)
- Click to "Edit Settings"
- Select the "Options" tab.
- In the list, under "Advanced," click "General"
- Over on the right, click the "Configuration Parameters..." button.
- Click the "Add Row" button.
- Make the new variable's name "keyboard.typematicMinDelay" and the value "2000000"
- Boot it back up.
Now you can login as "root," instead of "rrrroooooott."