Which product version are you using? I am using 2.3 Update 2 and intellisense does provide me with a list of class names or methods in the declaration.
If I enter
declare x as type string =
the list does not appear but if I enter a character such as 's' then the list will appear showing all matches. If I don't know what it starts with and I press Ctrl+space then the full list of available classes will appear.
Intellisense always displays a list of available method names after entering the ':' character.
I believe that the behavior you are describing occurred in versions prior to the current version.
Thanks.