I have some ideas that I got from the Game Maker documentation.
1.) Display a igh score list when the corresponding function function is called.
2.) Have functions for drawing health,energy, etc. by painting it or by using sprites.
3.) The ability to save local/global data when moving between .GED files.
4.) The ability to modify creation code per actor clone.
5.) The ability to save the gamer's progress in the game.
6.) The ability to create stand-alone executables in the freeware version.
7.) The abilty to access an actor from within another.
8.) Friction variable.
9.) Freezing the action in the game (pausing).
10.) The use of date and time in games.
11.) A built-in double linked list structure and functions to go with it.
12.) The ability to set more than one view and set their sizes.
13.) JOYSTICK SUPPORT!!!
14.) Default mouse cursor.
15.) Support for isometric games.
Note: I'm not trying to force all of these ideas on you at once, but I think that these are some things that no game design tool should be without.
(By the way, thank you for making such a great editor. Also, thanks for making a Linux version!)